Poly(vinyl acetal) resin compositions, layers, and interlayers having enhanced optical properties

ABSTRACT

Resin compositions, layers, and interlayers comprising two or more thermoplastic polymers and at least one RI balancing agent for adjusting the refractive index of at least one of the resins or layers is provided. Such compositions, layers, and interlayers exhibit enhanced optical properties while retaining other properties, such as impact resistance and acoustic performance.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/376,849 filed Dec. 13, 2016, now United States Publication Number2017-0087813, which is a continuation of U.S. patent application Ser.No. 14/563,364 filed on Dec. 8, 2014, now U.S. Pat. No. 9,522,517, thedisclosures of which are incorporated herein by reference in theirentirety.

BACKGROUND Field of the Invention

This disclosure relates to polymer resins and, in particular, to polymerresins suitable for use in polymer interlayers, including those utilizedin multiple layer panels.

Description of Related Art

Poly(vinyl butyral) (PVB) is often used in the manufacture of polymersheets that can be used as interlayers in multiple layer panels,including, for example, light-transmitting laminates such as safetyglass or polymeric laminates. PVB is also used in photovoltaic solarpanels to encapsulate the panels which are used to generate and supplyelectricity for commercial and residential applications.

Safety glass generally refers to a transparent laminate that includes atleast one polymer sheet, or interlayer, disposed between two sheets ofglass. Safety glass is often used as a transparent barrier inarchitectural and automotive applications, and one of its primaryfunctions is to absorb energy resulting from impact or a blow withoutallowing penetration of the object through the glass and to keep theglass bonded even when the applied force is sufficient to break theglass. This prevents dispersion of sharp glass shards, which minimizesinjury and damage to people or objects within an enclosed area. Safetyglass may also provide other benefits, such as a reduction inultraviolet (UV) and/or infrared (IR) radiation, and it may also enhancethe aesthetic appearance of window openings through addition of color,texture, and the like. Additionally, safety glass with desirableacoustic properties has also been produced, which results in quieterinternal spaces.

Often, polymers that exhibit one set of desirable properties, such asacoustic performance, lack other desirable properties, such as impactresistance or strength. Therefore, in order to achieve desirablecombinations of properties, multilayered polymer interlayers have beenused. These multilayered interlayers may include at least one inner“core” layer sandwiched between two outer “skin” layers. Often, the corelayer of an interlayer may be a softer layer having a lower glasstransition temperature, which enhances its acoustic performance.However, because such resin layers can be difficult to easily processand/or transport, the skin layers of such multilayered interlayers areoften stiffer, with higher glass transition temperatures, which impartsenhanced processability, strength, and impact resistance to theinterlayer.

However, use of various layers having different properties can alsoproduce optical defects within the interlayer. For example, one defectcommon to these types of multilayer interlayers is mottle. Mottle is anobjectionable form of optical distortion or visual defect appearing asuneven spots or texture, usually in the final structure. Mottle iscaused by small-scale surface variations at the interfaces between thesoft and stiff layers wherein the individual layers have differentrefractive indices. Clarity is another important optical property thatis determined by measuring the level of haze within the interlayer orpanel. High haze typically occurs when different types of opticallyincompatible polymers and/or plasticizers are blended or mixed together.In such mixtures, light passing through the blend is scattered as itencounters regions of different polymer materials, and the result is ahazy, visually unclear appearance. High clarity polymers and interlayersare those having very low haze values.

Thus, a need exists for polymer resins, resin layers, and interlayersthat exhibit desirable optical properties, such as reduced haze andmottle and improved clarity, without sacrificing other properties,including impact resistance and acoustic performance. Such interlayerscould be monolithic or multilayered and should be usable in a widevariety of applications, including safety glass and polymer laminates.

SUMMARY

One embodiment of the present invention concerns an interlayercomprising a first resin layer comprising a first poly(vinyl acetal)resin and a first plasticizer; a second resin layer adjacent to thefirst resin layer, wherein the second resin layer comprises a secondpoly(vinyl acetal) resin and a second plasticizer, wherein at least oneof the first poly(vinyl acetal) resin and the second poly(vinyl acetal)resin comprises residues of an aldehyde having a refractive index of atleast 1.421, and wherein the haze value of the interlayer is less than 5percent.

Another embodiment of the present invention concerns an interlayercomprising a first plasticized resin layer comprising a first poly(vinylacetal) resin; a second plasticized resin layer comprising a secondpoly(vinyl acetal) resin, wherein the second plasticized resin layer hasa refractive index of at least 1.470; and a third plasticized polyvinylresin layer comprising a third poly(vinyl acetal) resin, wherein thesecond plasticized resin layer is sandwiched between the firstplasticized resin layer and the third plasticized resin layer, andwherein the largest of the absolute value of the difference between therefractive index of the first plasticized resin layer and the refractiveindex of the second plasticized resin layer and the absolute value ofthe difference between the refractive index of the second plasticizedresin layer and the refractive index of the third plasticized resinlayer is not more than 0.010.

Yet another embodiment of the present invention concerns a method formaking an interlayer, the method comprising the steps of providing afirst resin layer comprising a first poly(vinyl acetal) resin and afirst plasticizer; providing a second resin layer comprising a secondpoly(vinyl acetal) resin and a second plasticizer; and assembling thefirst and the second resin layers into an interlayer, wherein the firstresin layer is adjacent to the second resin layer, wherein at least oneof the first and the second resin layers has a refractive index of atleast 1.470, and wherein the absolute value of the difference betweenthe refractive index of the first resin layer and the second resin layeris not more than 0.010.

DETAILED DESCRIPTION

Resin compositions, layers, and interlayers according to variousembodiments of the present invention can comprise one or morethermoplastic polymers and a refractive index (RI) balancing agent. Asused herein, the term “refractive index balancing agent” or “RIbalancing agent” refers to any component or additive included in thecomposition, layer, or interlayer for adjusting the refractive index ofat least one of the resins or layers. The RI balancing agent mayincrease or reduce the refractive index of at least one of the resins orlayers within an interlayer, which may improve the optical properties ofthe interlayer, including mottle, haze, and/or clarity, as compared toan identical interlayer formed without an RI balancing agent.

As used herein, the terms “polymer resin composition” and “resincomposition” refer to compositions including one or more polymer resins.Polymer compositions may optionally include other components, such asplasticizers and/or other additives. As used herein, the terms “polymerresin layer” and “resin layer” refer to one or more polymer resins,optionally combined with one or more plasticizers, that have been formedinto a polymeric sheet. Again, resin layers can include additionaladditives, although these are not required. As used herein, the term“interlayer” refers to a single or multiple layer polymer sheet suitablefor use with at least one rigid substrate to form a multiple layerpanel. The terms “single-sheet” interlayer and “monolithic” interlayerrefer to interlayers formed of one single resin sheet, while the terms“multiple layer” and “multilayer” interlayer refer to interlayers havingtwo or more resin sheets coextruded, laminated, or otherwise coupled toone another.

The resin compositions, layers, and interlayers described herein mayinclude one or more thermoplastic polymers. Examples of suitablethermoplastic polymers can include, but are not limited to, poly(vinylacetal) resins, polyurethanes (PU), poly(ethylene-co-vinyl) acetates(EVA), polyvinyl chlorides (PVC), poly(vinylchloride-co-methacrylate),polyethylenes, polyolefins, ethylene acrylate ester copolymers,poly(ethylene-co-butyl acrylate), silicone elastomers, epoxy resins, andacid copolymers such as ethylene/carboxylic acid copolymers and ionomersthereof, derived from any of the previously-listed polymers, andcombinations thereof. In some embodiments, the thermoplastic polymer canbe selected from the group consisting of poly(vinyl acetal) resins,polyvinyl chloride, and polyurethanes, or the resin can comprise one ormore poly(vinyl acetal) resins. Although described herein with respectto poly(vinyl acetal) resins, it should be understood that one or moreof the above polymer resins could be included with, or in the place of,the poly(vinyl acetal) resins described below in accordance with variousembodiments of the present invention.

When the resin compositions, layers, and interlayers described hereininclude poly(vinyl acetal) resins, the poly(vinyl acetal) resins can beformed according to any suitable method. Poly(vinyl acetal) resins canbe formed by acetalization of polyvinyl alcohol with one or morealdehydes in the presence of an acid catalyst. The resulting resin canthen be separated, stabilized, and dried according to known methods suchas, for example, those described in U.S. Pat. Nos. 2,282,057 and2,282,026, as well as “Vinyl Acetal Polymers,” in the Encyclopedia ofPolymer Science & Technology, 3^(rd) ed., Volume 8, pages 381-399, by B.E. Wade (2003). The resulting poly(vinyl acetal) resins may have a totalpercent acetalization of at least about 50, at least about 60, at leastabout 70, at least about 75, at least about 80, at least about 85 weightpercent, measured according to ASTM D-1396, unless otherwise noted. Thetotal amount of aldehyde residues in a poly(vinyl acetal) resin can becollectively referred to as the acetal component, with the balance ofthe poly(vinyl acetal) resin being residual hydroxyl and residualacetate groups, which will be discussed in further detail below.

According to some embodiments, the resin composition, layer, orinterlayer may include at least one poly(vinyl acetal) resin, which maybe present in the composition, layer, or interlayer in an amount of atleast about 0.5, at least about 1, at least about 2, at least about 3,at least about 5, at least about 10, at least about 15, at least about20, at least about 30, at least about 40, or at least about 45 weightpercent, based on the combined weight of all resins in the composition,layer, or interlayer. Together, the at least one poly(vinyl acetal)resins can make up at least about 10, at least about 20, at least about30, at least about 40, at least about 50, at least about 60, at leastabout 70, or at least about 80 weight percent of composition, layer, orinterlayer, based on the combined weight of all resins. In someembodiments, the amount of resins other than the at least one poly(vinylacetal) resin can be not more than about 20, not more than about 15, notmore than about 10, not more than about 5, not more than about 2, or notmore than about 1 weight percent, based on the combined weight of allresins.

In some embodiments, the resin composition, layer, or interlayer caninclude at least a first poly(vinyl acetal) resin and a secondpoly(vinyl acetal) resin, each of which may be present in thecomposition, layer, or interlayer in an amount of at least about 0.5, atleast about 1, at least about 2, at least about 3, at least about 5, atleast about 10, at least about 15, at least about 20, at least about 30,at least about 40, or at least about 45 weight percent, based on thecombined weight of all resins in the composition, layer, or interlayer.Together, the first and second poly(vinyl acetal) resins can make up atleast about 10, at least about 20, at least about 30, at least about 40,at least about 50, at least about 60, at least about 70, or at leastabout 80 weight percent of composition, layer, or interlayer, based onthe combined weight of all resins. In some embodiments, the amount ofresins other than the first and second poly(vinyl acetal) resins can benot more than about 20, not more than about 15, not more than about 10,not more than about 5, not more than about 2, or not more than about 1weight percent, based on the combined weight of all resins.

In some embodiments, one of the first and the second poly(vinyl acetal)resins can be present in the composition, layer, or interlayer in anamount of less than 12 weight percent, based on the combined weight ofthe first and second poly(vinyl acetal) resins. For example, the firstor the second poly(vinyl acetal) resin can be present in thecomposition, layer, or interlayer in an amount of at least about 0.5, atleast about 1, at least about 1.5, at least about 2, at least about 2.5,at least about 3, at least about 3.5, at least about 4, at least about4.5, at least about 5, at least about 5.5, at least about 6, at leastabout 6.5, at least about 7 weight percent and/or not more than about12, not more than about 11.5, not more than about 11, not more thanabout 10.5, not more than about 10, not more than about 9.5, not morethan about 9, not more than about 8.5, not more than about 8, not morethan about 7.5 weight percent, based on the combined weight of the firstand second poly(vinyl acetal) resins. In some embodiments, one of thefirst and second poly(vinyl acetal) resins can be present in thecomposition, layer, or interlayer in an amount in the range of fromabout 0.5 to about 12, about 1.5 to about 11.5, about 2 to about 11,about 2.5 to about 10 weight percent, based on the combined weight ofthe first and second poly(vinyl acetal) resins.

The first and second poly(vinyl acetal) resins can include residues ofany suitable aldehyde and, in some embodiments, can include residues ofat least one C₁ to C₁₀ aldehyde, at least one C₄ to C₈ aldehyde.Examples of suitable C₄ to C₈ aldehydes can include, but are not limitedto, n-butyraldehyde, iso-butyraldehyde, 2-methylvaleraldehyde, n-hexylaldehyde, 2-ethylhexyl aldehyde, n-octyl aldehyde, and combinationsthereof. At least one of the first and second poly(vinyl acetal) resinscan include at least about 20, at least about 30, at least about 40, atleast about 50, at least about 60, or at least about 70 weight percentof residues of at least one C₄ to C₈ aldehyde, based on the total weightof aldehyde residues of the resin, and/or can include not more thanabout 90, not more than about 85, not more than about 80, not more thanabout 75, not more than about 70, or not more than about 65 weightpercent of at least one C₄ to C₈ aldehyde, or in the range of from about20 to about 90, about 30 to about 80, or about 40 to about 70 weightpercent of at least one C₄ to C₈ aldehyde. The C₄ to C₈ aldehyde may beselected from the group listed above, or it can be selected from thegroup consisting of n-butyraldehyde, iso-butyraldehyde, 2-ethylhexylaldehyde, and combinations thereof.

In various embodiments, the first and/or second poly(vinyl acetal) resinmay be a polyvinyl n-butyral (PVB) resin. In other embodiments, thefirst and/or second poly(vinyl acetal) resin can be a poly(vinyln-butyral) resin that mainly comprises residues of n-butyraldehyde, andmay, for example, include not more than about 50, not more than about40, not more than about 30, not more than about 20, not more than about10, not more than about 5, or not more than about 2 weight percent ofresidues of an aldehyde other than n-butyraldehyde, based on the totalweight of all aldehyde residues of the resin. When the first and/orsecond poly(vinyl acetal) resins are PVB resins, the molecular weight ofthe resins can be at least about 50,000, at least about 70,000, at leastabout 100,000 Daltons and/or not more than about 600,000, not more thanabout 550,000, not more than about 500,000, not more than about 450,000,or not more than 425,000 Daltons, measured by size exclusionchromatography using low angle laser light scattering (SEC/LALLS) methodof Cotts and Ouano. As used herein, the term “molecular weight” refersto weight average molecular weight (Mw). The molecular weight of thefirst and/or second poly(vinyl acetal) resin can be in the range of fromabout 50,000 to about 600,000, about 70,000 to about 450,000, or about100,000 to about 425,000 Daltons.

Although generally described herein with respect to first and secondpoly(vinyl acetal) resins, it should be understood that, in someembodiments, an equivalent single poly(vinyl acetal) resin includingfirst and second acetal moieties may be substituted for the first andsecond poly(vinyl acetal) resins with similar results. As used herein,the term “poly(vinyl acetal) resin component” can refer to an individualpoly(vinyl acetal) resin present in a blend of resins or to an acetalmoiety present on a single poly(vinyl acetal) resin. In variousembodiments, the ratio, by weight, of the amount of the first poly(vinylacetal) resin component to the second poly(vinyl acetal) resin componentin a layer, interlayer, or blend can be in the range of from about0.5:99.5 to about 99.5:0.5, about 1:99 to 99:1, about 10:90 to about90:10, about 25:75 to about 75:25, or about 40:60 to about 60:40.

In some embodiments, at least one resin composition, layer, orinterlayer can include at least a first poly(vinyl acetal) resincomponent and a second poly(vinyl acetal) resin component. In someembodiments, the first and second resin components may comprise firstand second poly(vinyl acetal) resins that can be physically mixed toform a resin blend, which may be combined with one or more plasticizersor other additives to provide a blended resin layer or interlayer. Inother embodiments, the first and second poly(vinyl acetal) resincomponents may be present as respective first and second acetal moietiesin a single poly(vinyl acetal) resin. As with the resin blend, thissingle “hybrid” poly(vinyl acetal) resin can be optionally blended witha plasticizer and utilized in resin layers and interlayers.

In some embodiments, when the resin components include poly(vinylacetal) resins, the first and second poly(vinyl acetal) resins may beblended such that one of the first and second resins is dispersed withinthe other of the first and second resins, which can form domains of oneof the first and second poly(vinyl acetal) resins within the other ofthe first and second poly(vinyl acetal) resins. Such a blended resin maybe used as a single layer interlayer or it may be combined with one ormore adjacent layers to form a multilayer interlayer. In otherembodiments, the first and second poly(vinyl acetal) resins can bepresent in adjacent layers of a multilayer interlayer, such that one ofthe layers of the interlayer includes the first poly(vinyl acetal) resinand another layer of the interlayer includes the second poly(vinylacetal) resin. Additional layers can also be present adjacent to atleast one of the layers.

The resin compositions, layers, and interlayers according to variousembodiments of the present invention can further include at least oneplasticizer. Depending on the specific composition of the resin orresins in a composition, layer, or interlayer, the plasticizer may bepresent in an amount of at least about 5, at least about 10, at leastabout 15, at least about 20, at least about 25, at least about 30, atleast about 35, at least about 40, at least about 45, at least about 50,at least about 55, at least about 60 parts per hundred parts of resin(phr) and/or not more than about 120, not more than about 110, not morethan about 105, not more than about 100, not more than about 95, notmore than about 90, not more than about 85, not more than about 75, notmore than about 70, not more than about 65, not more than about 60, notmore than about 55, not more than about 50, not more than about 45, ornot more than about 40 phr, or in the range of from about 5 to about120, about 10 to about 110, about 20 to about 90, or about 25 to about75 phr. Specific embodiments are discussed in detail shortly.

As used herein, the term “parts per hundred parts of resin” or “phr”refers to the amount of plasticizer present as compared to one hundredparts of resin, on a weight basis. For example, if 30 grams ofplasticizer were added to 100 grams of a resin, the plasticizer would bepresent in an amount of 30 phr. If the resin composition, layer, orinterlayer includes two or more resins, the weight of plasticizer iscompared to the combined amount of all resins present to determine theparts per hundred resin. Further, when the plasticizer content of alayer or interlayer is provided herein, it is provided with reference tothe amount of plasticizer in the mix or melt that was used to producethe layer or interlayer.

Examples of suitable plasticizers can include, but are not limited to,triethylene glycol di-(2-ethylhexanoate) (“3GEH”), triethylene glycoldi-(2-ethylbutyrate), triethylene glycol diheptanoate, tetraethyleneglycol diheptanoate, tetraethylene glycol di-(2-ethylhexanoate)(“4GEH”), dihexyl adipate, dioctyl adipate, hexyl cyclohexyladipate,diisononyl adipate, heptylnonyl adipate, di(butoxyethyl) adipate, andbis(2-(2-butoxyethoxy)ethyl) adipate, dibutyl sebacate, dioctylsebacate, and mixtures thereof. The plasticizer may be selected from thegroup consisting of triethylene glycol di-(2-ethylhexanoate) andtetraethylene glycol di-(2-ethylhexanoate), or the plasticizer cancomprise triethylene glycol di-(2-ethylhexanoate).

According to some embodiments, the first and second poly(vinyl acetal)resins in the compositions, layers, and interlayers described herein canhave different compositions. For example, in some embodiments, the firstpoly(vinyl acetal) resin can have a residual hydroxyl content and/orresidual acetate content that is at least about 2, at least about 3, atleast about 4, at least about 5, at least about 6, or at least about 8weight percent higher or lower than the residual hydroxyl content and/orresidual acetate content of the second poly(vinyl acetal) resin. As usedherein, the terms “residual hydroxyl content” and “residual acetatecontent” refer to the amount of hydroxyl and acetate groups,respectively, that remain on a resin after processing is complete. Forexample, polyvinyl n-butyral can be produced by hydrolyzing polyvinylacetate to polyvinyl alcohol, and then acetalizing the polyvinyl alcoholwith n-butyraldehyde to form polyvinyl n-butyral. In the process ofhydrolyzing the polyvinyl acetate, not all of the acetate groups areconverted to hydroxyl groups, and residual acetate groups remain on theresin. Similarly, in the process of acetalizing the polyvinyl alcohol,not all of the hydroxyl groups are converted to acetal groups, whichalso leaves residual hydroxyl groups on the resin. As a result, mostpoly(vinyl acetal) resins include both residual hydroxyl groups (asvinyl hydroxyl groups) and residual acetate groups (as vinyl acetategroups) as part of the polymer chain. The residual hydroxyl content andresidual acetate content are expressed in weight percent, based on theweight of the polymer resin, and are measured according to ASTM D-1396,unless otherwise noted.

The difference between the residual hydroxyl content of the first andsecond poly(vinyl acetal) resins could also be at least about 2, atleast about 5, at least about 10, at least about 12, at least about 15,at least about 20, or at least about 30 weight percent. As used herein,the term “weight percent different” or “the difference . . . is at least. . . weight percent” refers to a difference between two given weightpercentages, calculated by subtracting the one number from the other.For example, a poly(vinyl acetal) resin having a residual hydroxylcontent of 12 weight percent has a residual hydroxyl content that is 2weight percent lower than a poly(vinyl acetal) resin having a residualhydroxyl content of 14 weight percent (14 weight percent−12 weightpercent=2 weight percent). As used herein, the term “different” canrefer to a value that is higher than or lower than another value.

At least one of the first and second poly(vinyl acetal) resins can havea residual hydroxyl content of at least about 14, at least about 14.5,at least about 15, at least about 15.5, at least about 16, at leastabout 16.5, at least about 17, at least about 17.5, at least about 18,at least about 18.5, at least about 19, at least about 19.5 and/or notmore than about 45, not more than about 40, not more than about 35, notmore than about 33, not more than about 30, not more than about 27, notmore than about 25, not more than about 22, not more than about 21.5,not more than about 21, not more than about 20.5, or not more than about20 weight percent, or in the range of from about 14 to about 45, about16 to about 30, about 18 to about 25, about 18.5 to about 20, or about19.5 to about 21 weight percent.

The other poly(vinyl acetal) resin can have a residual hydroxyl contentof at least about 8, at least about 9, at least about 10, at least about11 weight percent and/or not more than about 16, not more than about 15,not more than about 14.5, not more than about 13, not more than about11.5, not more than about 11, not more than about 10.5, not more thanabout 10, not more than about 9.5, or not more than about 9 weightpercent, or in the range of from about 8 to about 16, about 9 to about15, or about 9.5 to about 14.5 weight percent, and can be selected suchthat the difference between the residual hydroxyl content of the firstand second poly(vinyl acetal) resin is at least about 2 weight percent,as mentioned previously. One or more other poly(vinyl acetal) resins mayalso be present in the resin composition, layer, or interlayer and canhave a residual hydroxyl within the ranges provided above. Additionally,the residual hydroxyl content of the one or more other poly(vinylacetal) resins can be the same as or different than the residualhydroxyl content of the first and/or second poly(vinyl acetal) resins.

In some embodiments, at least one of the first and second poly(vinylacetal) resins can have a residual acetate content different than theother. For example, in some embodiments, the difference between theresidual acetate content of the first and second poly(vinyl acetal)resins can be at least about 2, at least about 3, at least about 4, atleast about 5, at least about 8, at least about 10 weight percent. Oneof the poly(vinyl acetal) resins may have a residual acetate content ofnot more than about 4, not more than about 3, not more than about 2, ornot more than about 1 weight percent, measured as described above. Insome embodiments, at least one of the first and second poly(vinylacetal) resins can have a residual acetate content of at least about 5,at least about 8, at least about 10, at least about 12, at least about14, at least about 16, at least about 18, at least about 20, or at leastabout 30 weight percent. The difference in the residual acetate contentbetween the first and second poly(vinyl acetal) resins can be within theranges provided above, or the difference can be less than about 3, notmore than about 2, not more than about 1, or not more than about 0.5weight percent. Additional poly(vinyl acetal) resins present in theresin composition or interlayer can have a residual acetate content thesame as or different than the residual acetate content of the firstand/or second poly(vinyl acetal) resin.

In some embodiments, the difference between the residual hydroxylcontent of the first and second poly(vinyl acetal) resins can be lessthan about 2, not more than about 1, not more than about 0.5 weightpercent and the difference in the residual acetate content between thefirst and second poly(vinyl acetal) resins can be at least about 3, atleast about 5, at least about 8, at least about 15, at least about 20,or at least about 30 weight percent. In other embodiments, thedifference in the residual acetate content of the first and secondpoly(vinyl acetal) resins can be less than about 3, not more than about2, not more than about 1, or not more than about 0.5 weight percent andthe difference in the residual hydroxyl content of the first and secondpoly(vinyl acetal) resins can be at least about 2, at least about 5, atleast about 10, at least about 12, at least about 15, at least about 20,or at least about 30 weight percent.

In various embodiments, the differences in residual hydroxyl and/orresidual acetate content of the first and second poly(vinyl acetal)resins can be selected to control or provide certain performanceproperties, such as strength, impact resistance, penetration resistance,processability, or acoustic performance to the final composition, layer,or interlayer. For example, poly(vinyl acetal) resins having a higherresidual hydroxyl content, usually greater than about 16 weight percent,can facilitate high impact resistance, penetration resistance, andstrength to a resin composition or layer, while lower hydroxyl contentresins, usually having a residual hydroxyl content of less than 16weight percent, can improve the acoustic performance of the interlayeror blend.

Poly(vinyl acetal) resins having higher or lower residual hydroxylcontents and/or residual acetate contents may also, when combined withat least one plasticizer, ultimately include different amounts ofplasticizer. As a result, layers or domains formed of first and secondpoly(vinyl acetal) resins having different compositions may also havedifferent properties within a single resin layer or interlayer. Althoughnot wishing to be bound by theory, it is assumed that the compatibilityof a given plasticizer with a poly(vinyl acetal) resin can depend, atleast in part, on the composition of the polymer, and, in particular, onits residual hydroxyl content. Overall, poly(vinyl acetal) resins withhigher residual hydroxyl contents tend to exhibit a lower compatibility(or capacity) for a given plasticizer as compared to similar resinshaving a lower residual hydroxyl content. As a result, poly(vinylacetal) resins with higher residual hydroxyl contents tend to be lessplasticized and exhibit higher stiffness than similar resins havinglower residual hydroxyl contents. Conversely, poly(vinyl acetal) resinshaving lower residual hydroxyl contents may tend to, when plasticizedwith a given plasticizer, incorporate higher amounts of plasticizer,which may result in a softer resin layer that exhibits a lower glasstransition temperature than a similar resin having a higher residualhydroxyl content. Depending on the specific resin and plasticizer, thesetrends could be reversed.

When two poly(vinyl acetal) resins having different levels of residualhydroxyl content are blended with a plasticizer, the plasticizer maypartition between the resin layers or domains, such that moreplasticizer can be present in the layer or domain having the lowerresidual hydroxyl content and less plasticizer may be present in thelayer or domain having the higher residual hydroxyl content. Ultimately,a state of equilibrium is achieved between the two resins. Thecorrelation between the residual hydroxyl content of a poly(vinylacetal) resin and plasticizer compatibility/capacity can facilitateaddition of a proper amount of plasticizer to the polymer resin. Such acorrelation also helps to stably maintain the difference in plasticizercontent between two or more resins when the plasticizer would otherwisemigrate between the resins.

In some embodiments, a resin layer or interlayer can include at least afirst resin layer comprising a first poly(vinyl acetal) resin and afirst plasticizer, and a second resin layer, adjacent to the first resinlayer, comprising a second poly(vinyl acetal) resin and a secondplasticizer. The first and second plasticizer can be the same type ofplasticizer, or the first and second plasticizers may be different. Insome embodiments, at least one of the first and second plasticizers mayalso be a blend of two or more plasticizers, which can be the same as ordifferent than one or more other plasticizers. When one of the first andsecond poly(vinyl acetal) resins has a residual hydroxyl content that isat least 2 weight percent higher or lower than the residual hydroxylcontent of the other, the difference in plasticizer content between theresin layers can be at least about 2, at least about 5, at least about8, at least about 10, at least about 12, or at least about 15 phr. Inmost embodiments, the resin layer that includes the resin having a lowerhydroxyl content can have the higher plasticizer content. In order tocontrol or retain other properties of the resin layer or interlayer, thedifference in plasticizer content between the first and second resinlayers may be not more than about 40, not more than about 30, not morethan about 25, not more than about 20, or not more than about 17 phr. Inother embodiments, the difference in plasticizer content between thefirst and second resin layers can be at least about 40, at least about50, at least about 60, or at least about 70 phr.

As a result, in some embodiments, wherein the first and secondpoly(vinyl acetal) resins are present in adjacent layers of a multilayerinterlayer, the first and second resin layers can exhibit differentglass transition temperatures. Similarly, when the first and secondpoly(vinyl acetal) resins are present in a blend, the domains of one ofthe first and second poly(vinyl acetal) resins can exhibit a differentglass transition temperature than the other of the first and secondpoly(vinyl acetal) resins. Glass transition temperature, or T_(g), isthe temperature that marks the transition from the glass state of thepolymer to the rubbery state. The glass transition temperatures of theresins and layers described herein were determined by dynamic mechanicalthermal analysis (DTMA). The DTMA measures the storage (elastic) modulus(G′) in Pascals, loss (viscous) modulus (G″) in Pascals, and the tandelta (G″/G′) of the specimen as a function of temperature at a givenoscillation frequency and temperature sweep rate. The glass transitiontemperature is then determined by the position of the tan delta peak onthe temperature scale. Glass transition temperatures provided hereinwere determined at an oscillation frequency of 1 Hz under shear mode anda temperature sweep rate of 3° C./min.

The difference in the glass transition temperature of the first resinlayer and the second resin layer, or between various regions of ablended resin or resin layer, can be at least about 3, at least about 5,at least about 8, at least about 10, at least about 12, at least about15, at least about 18, at least about 20, at least about 22, or at leastabout 25° C. One of the first and second resin layers can have a glasstransition temperature of at least about 26, at least about 28, at leastabout 30, at least about 33, at least about 35° C. and/or not more thanabout 70, not more than about 65, not more than about 60, not more thanabout 55, not more than about 50° C., or in the range of from about 26to about 70, about 30 to about 60, about 35 to about 50° C. The other ofthe first and second poly(vinyl acetal) resins can have a glasstransition temperature of not more than 25, not more than about 20, notmore than about 15, not more than about 10, not more than about 5, notmore than about 0, not more than about −5, or not more than about −10°C.

When the first and second poly(vinyl acetal) resins are blended with oneanother such that domains of one resin are dispersed within the other,such differences in plasticizer content and/or glass transitiontemperature may also exist between domains of the first and secondresins. For example, in some embodiments, a resin layer or interlayermay include various domains of higher or lower plasticizer contentand/or domains having higher or lower glass transition temperatures, asdescribed previously. In some embodiments, at least a portion of theresin layer or interlayer can have a glass transition temperature of atleast about 26, at least about 28, at least about 30, at least about 33,at least about 35° C. and/or not more than about 70, not more than about65, not more than about 60, not more than about 55, not more than about50° C., or in the range of from about 26 to about 70, about 28 to about60, about 35 to about 50° C. and/or at least a portion of the resinlayer or interlayer can have a glass transition temperature of not morethan 25, not more than about 20, not more than about 15, not more thanabout 10, not more than about 5, not more than about 0° C., not morethan about −5° C., or not more than about −10° C.

One or more resin blends, layers, and interlayers described herein mayinclude various other additives to impart particular properties orfeatures to the interlayer. Such additives can include, but are notlimited to, dyes, pigments, stabilizers such as ultraviolet stabilizers,antioxidants, anti-blocking agents, flame retardants, IR absorbers orblockers such as indium tin oxide, antimony tin oxide, lanthanumhexaboride (LaB₆) and cesium tungsten oxide, processing aides, flowenhancing additives, lubricants, impact modifiers, nucleating agents,thermal stabilizers, UV absorbers, dispersants, surfactants, chelatingagents, coupling agents, adhesives, primers, reinforcement additives,and fillers.

Additionally, various adhesion control agents (“ACAs”) can be used inthe interlayers of the present disclosure to control the adhesion of thesheet to glass. In various embodiments, the amount of ACAs present in aresin composition, layer, or interlayer can be at least about 0.003, atleast about 0.01, at least about 0.025 and/or not more than about 0.15,not more than about 0.10, or not more than about 0.04 phr, or in therange of from about 0.003 to about 0.15, about 0.01 to about 0.10, orabout 0.025 to about 0.04 phr. Suitable ACAs can include, but are notlimited to, sodium acetate, potassium acetate, magnesium bis(2-ethylbutyrate), magnesium bis(2-ethylhexanoate), and combinations thereof, aswell as the ACAs disclosed in U.S. Pat. No. 5,728,472.

Resins having different compositions and plasticized resin layers havingdifferent properties also tend to exhibit different refractive indices,which can reduce the optical quality of the resulting layer or blend.Although not wishing to be bound by theory, it is believed that suchdifferences in refractive index may cause light that passes through thedifferent resin layers or domains to be refracted in differentdirections, which may cause haze in the final product. At times, theabsolute value of the difference between the refractive index of thefirst poly(vinyl acetal) resin or layer and the refractive index of thesecond poly(vinyl acetal) resin or layer, measured according to ASTMD542 at a wavelength of 589 nm and 25° C., can exceed 0.010. As aresult, these compositions, layers, or interlayers can have a haze valuegreater than 5 percent and/or a mottle value greater than 3.

However, in various embodiments of the present invention, compositions,layers, and interlayers comprising a poly(vinyl acetal) resin mayfurther include at least one refractive index (RI) balancing agent foradjusting the refractive index of the composition, layer, or interlayer.In some embodiments, the composition, layer, or interlayer may includeat least a first poly(vinyl acetal) resin and a second poly(vinylacetal) resin along with at least one RI balancing agent. In otherembodiments, the composition, layer, or interlayer ma include a singlepoly(vinyl acetal) resin along with at least one RI balancing agent. Asdiscussed above, the RI balancing agent can be any suitable agentpresent in a resin or a resin blend, layer, or interlayer, or portionthereof, that increases or reduces the refractive index of at least oneresin or layer, which may improve the optical properties of theinterlayer as compared to an identical interlayer formed without an RIbalancing agent. In some embodiments, the resin blend, layer, orinterlayer may have a haze value of at least 5 percent when formed inthe absence of the RI balancing agent.

The RI balancing agent can be in any suitable form and may be physicallyblended with one or more resins or it can be chemically bonded, orreacted, with at least one resin so that the RI balancing agent isincorporated into the polymer chain. Examples of RI balancing agents caninclude, but are not limited to, liquid RI additives, solid RIadditives, and residues of at least one aldehyde present in one or moreof the poly(vinyl acetal) resins. Various embodiments of RI balancingagents, as well as resin compositions, layers, and interlayers includingthe same, will now be discussed in detail below.

The RI balancing agent may be present in the resin, resin layer, orinterlayer in an amount sufficient to modify the refractive index ofpoly(vinyl acetal) resin, resin layer, or interlayer. The RI balancingagent may also be present in the composition, layer, or interlayer in anamount sufficient to modify the refractive index of at least one of thetwo poly(vinyl acetal) resins, thereby minimizing the difference betweenthe refractive indices of two poly(vinyl acetal) resin layers havingdifferent refractive indices. The RI balancing agent may also minimizethe difference between the refractive index of one or more poly(vinylacetal) resins and one or more plasticizers within a resin composition,layer, or interlayer. In some embodiments, the RI balancing agent may bepresent in an amount sufficient to reduce the absolute value of thedifference between the refractive index the first poly(vinyl acetal)resin layer and the refractive index of the second poly(vinyl acetal)resin layer to not more than 0.010, not more than about 0.009, not morethan about 0.008, not more than about 0.007, not more than about 0.006,not more than about 0.005, not more than about 0.004, or not more thanabout 0.003. When a multilayer interlayer includes two or more resinlayers, the RI balancing agent may be present in one or both layers andcan, in some embodiments, be present in one of the layers in a higheramount than in one or more of the other layers.

In some embodiments, the RI balancing agent can comprise one or moreresidues of an aldehyde having a refractive index of at least 1.421, asmeasured by ASTM D542 at a wavelength of 589 nm and a temperature of 25°C. The RI balancing aldehyde, which may also be referred to herein as a“high refractive index aldehyde” or “high RI aldehyde,” can have arefractive index of at least about 1.425, at least about 1.450, at leastabout 1.475, at least about 1.500, at least about 1.510, or at leastabout 1.515 and/or not more than about 1.675, not more than about 1.650,or not more than about 1.625, or in the range of from about 1.425 toabout 1.675, about 1.475 to about 1.650, or about 1.515 to about 1.625.The high RI aldehyde may be an aromatic aldehyde that includes at leastone aromatic ring or group. Examples of aromatic aldehydes can include,but are not limited to, C₇ to C₃₀ aromatic aldehydes, C₈ to C₂₅ aromaticaldehydes, or C₉ to C₂₀ aromatic aldehydes. Specific examples of high RIaldehydes that can be used as RI balancing agents in various embodimentsof the present invention are listed in Table 1, below.

TABLE 1 Exemplary High RI Aldehydes Aldehyde Refractive IndexHexylcinnamaldehyde 1.517 Benzaldehyde 1.545 Cinnamaldehyde 1.6204-Chlorobenzaldehyde 1.585 4-t-butylphenylacetaldehyde 1.5302-phenylpropionaldehyde 1.517 Hydrocinnamaldehyde 1.523

When the RI balancing agent includes residues of at least one high RIaldehyde, at least one of the first and second poly(vinyl acetal) resinscan include residues of at least one high RI aldehyde in an amount of atleast about 0.5, at least about 1, at least about 5, at least about 10,at least about 15, at least about 20, at least about 25, at least about30, at least about 35, at least about 40, at least about 45, at leastabout 50, at least about 55, at least about 60, at least about 65, atleast about 70, at least about 75, at least about 80, at least about 85,at least about 90, at least about 95 percent and/or not more than about99.5, not more than about 99, not more than about 97, not more thanabout 95, not more than about 90, not more than about 85, not more thanabout 80, not more than about 75, not more than about 70, not more thanabout 65, or not more than about 60 weight percent, based on the totalweight of aldehyde residues of the first or second poly(vinyl acetal)resin. At least one of the first and second poly(vinyl acetal) resinscan include residues of at least one high RI aldehyde in an amount inthe range of from about 0.5 to about 99.5, about 10 to about 90, about25 to about 75, or about 40 to about 60 weight percent, based on thetotal weight of aldehyde residues of the first or second poly(vinylacetal) resin.

The amount of high RI aldehyde residues can be determined using acombination of Fourier Transform Infrared Spectroscopy (FT-IR) and SizeExclusion Chromatography (SEC) with UV detection. In particular, FT-IRis used to measure residual hydroxyl of the resin and SEC is used todetermine the amount of high RI aldehyde residues, with the amount ofany other aldehyde residues being determined by the difference. TheFT-IR analysis is performed using a Perkin Elmer Spectrum 100 FT-IRSpectrometer (commercially available from Perkin Elmer, Waltham, Mass.)with an ATR sampling attachment. The analysis is performed using 8 scansat a 4 cm−1 resolution. Prior to testing, a calibration is generatedfrom several poly(vinyl n-butyral) samples of varying residual hydroxylwhich have been dried in a desiccator with silica overnight at roomtemperature to remove excess moisture. The peak maximum wave number ofthe hydroxyl stretching band are correlated with the molar vinyl alcoholcontent of each sample, which was previously determined by ASTM D1396,and the resulting linear curve fits are used to predict molar residualhydroxyl content of the samples being analyzed. These values can beconverted to weight percent by calculation after determination of thecomposition of the poly(vinyl acetal) resin using SEC analysis has beencompleted, as described below.

The SEC analysis is performed using a Waters 2695 Alliance pump andautosampler with a Waters 410 inline differential refractive indexdetector and a Waters 2998 PDA inline UV detector (commerciallyavailable from Waters Corporation, Milford, Mass.) with DionexChromeleon v. 6.8 data acquisition software with an extension pack(commercially available from Thermo Fischer Scientific, Sunnyvale,Calif.). The analysis is performed with a PL Gel Mixed C (5 micron)column and Mixed E (3 micron) columns with an injection volume of 50microliters at a flow rate of 1.0 mL/minute. Samples are prepared bydissolving between 0.03 and 0.09 grams of resin in 10-15 mL ofstabilized tetrahydrofuran and then filtering each through a 0.22 micronPTFE filter. Initial calibrations of the chromatograph are performedusing a narrow molecular weight polystyrene standard and a poly(vinylacetal) resin including only residues of the high RI aldehyde, andsubsequent samples were calibrated with a broad molecular weightpolystyrene (commercially available as PSBR250K from American PolymerStandard Corporation, Mentor, Ohio).

In some embodiments, only one of the first and second poly(vinyl acetal)resins includes residues of the high RI aldehyde, while, in otherembodiments, both of the resins may include such residues. Therefractive index of a resin comprising residues of a high RI aldehydecan be at least about 1.492, at least about 1.495, at least about 1.500,at least about 1.505, at least about 1.510, or at least about 1.515.

In various embodiments, at least one of the first and second poly(vinylacetal) resins may also include residues of at least one aldehyde havinga refractive index of less than 1.421. Examples of these aldehydes caninclude, for example, aliphatic aldehydes such as the C₄ to C₈ aldehydesdiscussed above. The aldehydes having a refractive index of less than1.421 can be selected from the group consisting of n-butyraldehyde,iso-butyraldehyde, and 2-ethylhexyl aldehyde.

When these residues are present, the first and/or second poly(vinylacetal) resin can include at least about 10, at least about 15, at leastabout 20, at least about 25, at least about 30, at least about 35, atleast about 40, at least about 45, at least about 50, at least about 55,at least about 60, at least about 65, at least about 70, at least about75, at least about 80, at least about 85, at least about 90, at leastabout 95 percent and/or not more than about 99, not more than about 97,not more than about 95, not more than about 90, not more than about 85,not more than about 80, not more than about 75, not more than about 70,not more than about 65, or not more than about 60 weight percent, ofthese aldehydes, based on the total weight of aldehyde residues of thefirst or second poly(vinyl acetal) resin.

The amount of residues of an aldehyde having a refractive index of lessthan 1.421 are determined using the FT-IR/SEC method described above andthen by calculation according to the following formula: 100 weightpercent—weight percent residual hydroxyl (from FT-IR)—weight percent ofhigh RI aldehyde residues (from SEC)—weight percent residual acetate(from FT-IR)=weight percent of residues of aldehyde having refractiveindex less than 1.421. The first and/or second poly(vinyl acetal) resincan include residues of an aldehyde having a refractive index of lessthan 1.421 in an amount in the range of from about 10 to about 99, about25 to about 75, or about 40 to about 60 weight percent, based on thetotal weight of aldehyde residues of the first or second poly(vinylacetal) resin. The refractive index of one of these resins can be lessthan about 1.492, less than about 1.491, or less than about 1.490,measured as described previously.

According to some embodiments, one of the first and second poly(vinylacetal) resins primarily includes residues of a high RI aldehyde, whilethe other of the first and second poly(vinyl acetal) resins primarilyincludes residues of at least one aldehyde having a refractive index ofless than 1.421. As used herein, the term “primarily” means at least 75weight percent, so that a poly(vinyl acetal) resin primarily includingresidues of a specified aldehyde includes at least 75 weight percent ofresidues of the specified aldehyde, based on the total weight ofaldehyde residues of that resin. The poly(vinyl acetal) resin primarilyincluding residues of a high RI aldehyde can include not more than about25, not more than about 20, not more than about 15, not more than about10, not more than about 5, not more than about 2, or not more than about1 weight percent of residues of other aldehydes having a refractiveindex less than 1.421, based on the total weight of aldehyde residues ofthe resin.

Similarly, the other poly(vinyl acetal) resin, which can primarilyinclude residues of an aldehyde having a refractive index of less than1.421, may comprise not more than about 25, not more than about 20, notmore than about 15, not more than about 10, not more than about 5, notmore than about 2, or not more than about 1 weight percent of residuesof a high RI aldehyde, based on the total weight of aldehyde residues ofthe resin, and may include at least about 75, at least about 80, atleast about 85, at least about 90, at least about 95, at least about 97,or at least about 99 percent of residues of one or more aldehydes havinga refractive index less than 1.421. In some embodiments, the ratio ofthe resin primarily including residues of the high RI aldehyde to theother resin or resins in the composition can be at least about 1:99, atleast about 5:95, at least about 10:90, at least about 20:80, at leastabout 25:75, at least about 30:70, at least about 40:60 and/or not morethan about 99:1, not more than about 95:5, not more than about 90:10,not more than about 85:15, not more than about 75:25, not more thanabout 70:30, or not more than about 60:40, or in the range of from about1:99 to 99:1, about 10:90 to about 90:10, about 25:75 to 75:25, or about40:60 to 60:40.

In other embodiments, at least one of the first and second poly(vinylacetal) resins includes residues of a high RI aldehyde and at least onealdehyde having a refractive index of less than 1.421, thereby forming a“hybrid” resin that includes residues of both high and low RI aldehydes.According to these embodiments, the amounts of the high RI aldehyderesidues and the residues of aldehydes having a refractive index of lessthan 1.421, as well as the weight ratios of one to the other, in thehybrid resin can be within the same ranges provided above with respectto the resin blends. When the first or second poly(vinyl acetal) resinincludes residues of both high RI and lower RI aldehydes, the other ofthe two poly(vinyl acetal) resins may also include residues of at leastone high RI aldehyde. Alternatively, the other of the two resins mayinclude little or no high RI aldehyde residues, such that it includesless than about 10, less than about 5, less than about 2, or less thanabout 1 weight percent of residues of a high RI aldehyde, with thebalance being residues of an aldehyde having a refractive index of lessthan 1.421, including, for example, aldehydes selected from the groupconsisting of n-butyraldehyde, iso-butyraldehyde, 2-ethylhexyl aldehyde,and combinations thereof.

When the interlayer is a multilayer interlayer, it can include at leastone resin layer having at least a first poly(vinyl acetal) resin andanother resin layer comprising at least a second poly(vinyl acetal)resin, wherein the difference between the residual hydroxyl content ofthe first poly(vinyl acetal) resin and the second poly(vinyl acetal)resin is at least 2 weight percent. One or both of the poly(vinylacetal) resins can include residues of a high RI aldehyde and one of theresin layers may have a refractive index that is higher or lower thanthe other by at least about 0.002, at least about 0.003, at least about0.004 and/or not more than about 0.010, not more than about 0.009, notmore than about 0.008, or not more than about 0.007, or by an amount inthe range of from about 0.002 to about 0.010, about 0.003 to about0.009, or about 0.004 to about 0.007. In some embodiments when theinterlayer includes at least three resin layers, the innermost resinlayer can have the higher refractive index, while in other embodiments,the refractive index of one or both of the outer resin layers may behigher. In some embodiments, only one of the first and second poly(vinylacetal) resins may include residues of the high RI aldehyde. In otherembodiments, both of the poly(vinyl acetal) resins may include residuesof at least one high RI aldehyde, but the resins can still exhibit adifference in refractive index within the ranges provided above.

One or both of the poly(vinyl acetal) resins can include residues of atleast one high RI aldehyde. In some embodiments, when the poly(vinylacetal) resin including such residues has a residual hydroxyl content ofnot more than, for example, 15 weight percent, the resin layer includingsuch a resin may have a glass transition temperature of less than 20,not more than about 15, not more than about 10, not more than about 5,not more than about 0, not more than about −5, or not more than about−10° C. and a refractive index of at least about 1.465, at least about1.470, at least about 1.475, at least about 1.480, at least about 1.485,or at least about 1.490, each measured as described previously. Theplasticizer content of the layer, according to various embodiments, canbe at least about 50, at least about 55, at least about 60, at leastabout 65 phr and/or not more than about 120, not more than about 110,not more than about 90, not more than about 85, not more than about 80,or not more than about 75 phr, or in the range of from about 50 to about120, about 55 to about 110, about 60 to about 90, or about 65 to about75 phr.

When the resin having the residues of a high RI aldehyde in themultilayer interlayer discussed above has a residual hydroxyl contentgreater than, for example 16 weight percent, the resin layer includingthat resin may have a glass transition temperature of at least about 26,at least about 30, at least about 33, or at least about 35° C., and arefractive index of at least about 1.470, at least about 1.475, at leastabout 1.480, at least about 1.485, or at least about 1.490, eachmeasured as described previously. The plasticizer content of the layer,according to some embodiments, can be less than 50 phr, not more thanabout 45 phr, not more than about 40 phr, not more than about 30, notmore than about 20 phr.

According to various embodiments of the present invention, the RIbalancing agent can comprise a liquid RI balancing agent. As usedherein, the term “liquid RI balancing agent” refers to an RI balancingagent that is liquid at standard conditions of 25° C. and 1 atm. In someembodiments, the liquid RI balancing agent can be, for example, a highRI plasticizer. As used herein, the term “high RI plasticizer,” refersto a plasticizer having a refractive index of at least 1.460, measuredas described previously. The high RI plasticizers suitable for use as RIbalancing agents can have a refractive index of at least about 1.470, atleast about 1.480, at least about 1.490, at least about 1.500, at leastabout 1.510, at least about 1.520 and/or not more than about 1.600, notmore than about 1.575, or not more than about 1.550, measured asdiscussed above. The refractive index of the high RI plasticizers may bein the range of from about 1.460 to about 1.600, about 1.470 to about1.575, about 1.480 to about 1.550, about 1.490 to about 1.525.

Examples of types or classes of high RI plasticizers can include, butare not limited to, polyadipates (RI of about 1.460 to about 1.485);epoxides such as epoxidized soybean oils (RI of about 1.460 to about1.480); phthalates and terephthalates (RI of about 1.480 to about1.540); benzoates and toluates (RI of about 1.480 to about 1.550); andother specialty plasticizers (RI of about 1.490 to about 1.520).Specific examples of suitable RI plasticizers can include, but are notlimited to, dipropylene glycol dibenzoate, tripropylene glycoldibenzoate, polypropylene glycol dibenzoate, isodecyl benzoate,2-ethylhexyl benzoate, diethylene glycol benzoate, butoxyethyl benzoate,butoxyethyoxyethyl benzoate, butoxyethoxyethoxyethyl benzoate, propyleneglycol dibenzoate, 2,2,4-trimethyl-1,3-pentanediol dibenzoate,2,2,4-trimethyl-1,3-pentanediol benzoate isobutyrate, 1,3-butanedioldibenzoate, diethylene glycol di-o-toluate, triethylene glycoldi-o-toluate, dipropylene glycol di-o-toluate, 1,2-octyl dibenzoate,tri-2-ethylhexyl trimellitate, di-2-ethylhexyl terephthalate, bis-phenolA bis(2-ethylhexaonate), di-(butoxyethyl) terephthalate,di-(butoxyethyoxyethyl) terephthalate, and mixtures thereof. The high RIplasticizer may be selected from dipropylene glycol dibenzoate andtripropylene glycol dibenzoate, and/or 2,2,4-trimethyl-1,3-pentanedioldibenzoate.

When the resin layer or interlayer includes a high RI plasticizer, theplasticizer can be present in the layer alone or it can be blended withone or more additional plasticizers. The other plasticizer orplasticizers may also comprise high RI plasticizers, or one or more maybe a lower RI plasticizer having a refractive index of less than 1.460.In some embodiments, the lower RI plasticizer may have a refractiveindex of less than about 1.450, less than about 1.445, or less thanabout 1.442 and can be selected from the group listed previously. When amixture of two or more plasticizers are employed as a RI balancingagent, the mixture can have a refractive index within one or more of theabove ranges.

When used as an RI balancing agent in a multilayer interlayer, a high RIplasticizer may be present in different amounts in two or more of theresin layers. Similarly, when used as an RI balancing agent in a resincomposition or blended resin layer, the high RI plasticizer may bepartitioned as described previously, such that resin layers or domainshaving a lower residual hydroxyl content may have higher amounts of thehigh RI plasticizer. In some embodiments, at least one layer or portionof a resin layer or interlayer may comprise a high RI plasticizer as anRI balancing agent in an amount of at least about 5, at least about 10,at least about 15, at least about 20, at least about 25, at least about30, at least about 35 and/or not more than about 50, not more than about45, or not more than about 40 phr. The high RI plasticizer can bepresent in the resin layer or interlayer in an amount in the range offrom about 5 to about 50, about 10 to about 45, about 20 to about 40phr. In some embodiments, one or more other layers or portions caninclude the high RI plasticizer in an amount of at least about 50, atleast about 55, at least about 60, at least about 65, at least about 70and/or not more than about 120, not more than about 110, not more thanabout 100, not more than about 90, or not more than about 75 phr, or inthe range of from about 50 to about 120, about 55 to about 110, about 60to about 90, about 65 to about 75 phr. These amounts may include anyother plasticizers present in the composition, including those having arefractive index less than 1.460, or may include only the high RIplasticizer.

When a high RI plasticizer is used as an RI balancing agent in amultilayer interlayer, the interlayer can include at least one resinlayer having a first poly(vinyl acetal) resin and another resin layercomprising a second poly(vinyl acetal) resin, wherein the differencebetween the residual hydroxyl content of the first poly(vinyl acetal)resin and the second poly(vinyl acetal) resin is at least 2 weightpercent. At least one of the resin layers can include a high RIplasticizer in an amount sufficient so that the absolute value of thedifference between the refractive index of the resin layer and therefractive index of the another resin layer is not more than 0.010. Insome embodiments when the interlayer includes at least three resinlayers, the innermost resin layer can have a higher refractive index,while in other embodiments, the refractive index of one or both of theouter resin layers may be higher.

When a high RI plasticizer is included in a resin layer that includes atleast one poly(vinyl acetal) resin having the lower residual hydroxylcontent, at least a portion of the resin layer can have a glasstransition temperature of not more than 25, not more than about 20, notmore than about 15, not more than about 10, not more than about 5, notmore than about 0, not more than about −5, or not more than about −10°C., and the layer can have a refractive index of at least about 1.465,at least about 1.470, at least about 1.475, at least about 1.480, atleast about 1.485, or at least about 1.490, measured as describedpreviously. The plasticizer content of this layer, in some embodiments,can be at least about 50, at least about 55, at least about 60 phrand/or not more than about 120, not more than about 110, not more thanabout 90, not more than about 85, not more than about 80, or not morethan about 75 phr, or in the range of from about 50 to about 120, about55 to about 110, about 60 to about 90, or about 60 to about 75 phr.

When the high RI plasticizer is present in the resin layer thatcomprises the poly(vinyl acetal) resin having a higher residual hydroxylcontent, at least a portion of the layer can have a glass transitiontemperature of at least about 26, at least about 30, at least about 33,or at least about 35° C., and the layer can have a refractive index ofat least about 1.470, at least about 1.475, at least about 1.480, atleast about 1.485, or at least about 1.490, measured as describedpreviously. The plasticizer content of this layer, according to someembodiments, can be less than 50 phr, not more than about 45 phr, notmore than about 40 phr, not more than about 30, or not more than about20 phr.

According to various embodiments of the present invention, the RIbalancing agent may be a solid RI additive present in one or more layersor portions of a layer or interlayer. As used herein, the term “solid RIadditive” refers to an additive used to adjust the refractive index of apoly(vinyl acetal) resin, resin layer, or interlayer and which is solidat ambient conditions of 25° C. and 1 atm. In various embodiments, thesolid RI additive may have a melting point of at least about 27, atleast about 30, at least about 35, at least about 40, at least about 45,at least about 50, at least about 55, at least about 60, at least about75, at least about 80, at least about 85, at least about 90, at leastabout 95, or at least about 100° C. When employed in a resin blend,layer, or interlayer, the solid RI additive can be present in an amountsufficient such that the absolute value of the difference between therefractive indices of the first and second resin layers is not more thanabout 0.010. The difference between the refractive index of the firstand second resin layers may be greater than 0.010, when formulated intoidentical resin layers in the absence of the solid RI additive.

In some embodiments, the solid RI additive can be a high RI solidadditive for increasing the refractive index of at least one resin layeror interlayer. The refractive index of the high RI solid additive can beat least about 1.460, at least about 1.465, at least about 1.470, atleast about 1.475, at least about 1.480, at least about 1.485, at leastabout 1.490, at least about 1.495, at least about 1.500, at least about1.505, at least about 1.510, at least about 1.525, at least about 1.550,at least about 1.575, or at least about 1.600, measured as describedpreviously. In other embodiments, the solid RI additive may be a RIlowering solid additive for reducing the refractive index of at leastone resin or resin layer. The RI lowering solid additive can have arefractive index of less than 1.460, not more than about 1.455, not morethan about 1.450, not more than about 1.445, or not more than about1.440, measured as described previously. Whether higher or lower, thesolid RI additive can have a refractive index that is at least about0.005, at least about 0.010, at least about 0.050, at least about 0.10and/or not more than about 0.50, not more than about 0.35, or not morethan about 0.20 different than the refractive index of the poly(vinylacetal) resin. The difference in refractive index between the solid RIadditive and the poly(vinyl acetal) resin can be in the range of fromabout 0.005 to about 0.50, about 0.010 to about 0.35, or about 0.050 toabout 0.35.

In various embodiments, the solid RI additive can be present in a resincomposition or interlayer in an amount of at least about 0.5, at leastabout 1, at least about 1.5, at least about 2, or at least about 5 phr,depending on the specific type of additive and layer or interlayer. Thesolid RI additive, whether a high RI additive or an RI loweringadditive, may comprise a physical solid RI additive capable of beingphysically mixed or blended with at least one poly(vinyl acetal) resinin a resin composition or layer, or it can be a reactive solid RIadditive, which may react with and become incorporated into the backboneof one or more poly(vinyl acetal) resins.

The solid RI additive can be used in combination with one or more low RIplasticizers. Examples of low RI plasticizers can include, but are notlimited to, triethylene glycol di-(2-ethylhexanoate) (“3GEH”),triethylene glycol di-(2-ethylbutyrate), triethylene glycoldiheptanoate, tetraethylene glycol diheptanoate, tetraethylene glycoldi-(2-ethylhexanoate) (“4GEH”), dihexyl adipate, dioctyl adipate, hexylcyclohexyladipate, diisononyl adipate, heptylnonyl adipate,di(butoxyethyl) adipate, and bis(2-(2-butoxyethoxy)ethyl) adipate,dibutyl sebacate, dioctyl sebacate, and mixtures thereof. Theplasticizer may be selected from the group consisting of triethyleneglycol di-(2-ethylhexanoate) and tetraethylene glycoldi-(2-ethylhexanoate), or the plasticizer can comprise triethyleneglycol di-(2-ethylhexanoate). The solid RI additive can also be used incombination with one or more high RI plasticizers mentioned previously.

When the solid RI additive is a physical solid RI additive, it may becombined with one or more poly(vinyl acetal) resins or layers in aninterlayer. In some embodiments, the physical solid RI additive may bepresent in at least one layer or in an interlayer in an amount of atleast about 1, at least about 2, at least about 3, at least about 5, atleast about 8, at least about 10, at least about 12, at least about 15,at least about 20 and/or not more than about 60, not more than about 55,not more than about 50, not more than about 45, not more than about 40,not more than about 35, not more than about 30, not more than about 25,not more than about 20, or not more than about 15 phr, or in an amountin the range of from about 1 to about 60, about 5 to about 50, or about10 to about 45 phr. Examples of suitable physical solid high RIadditives can include, but are not limited to, polyadipates, polystyrenehaving a molecular weight of less than 2500, epoxides, phthalic acidesters, benzoic acid esters, inorganic oxides such as, for example,zirconium oxide, and combinations thereof. Physical solid RI loweringadditives can be selected from the group consisting of halogenatedadditives, and silicon-containing additives.

When utilized in a multilayer interlayer, the physical solid RI additivemay be present in one of the resin layers in a higher amount than one ormore other layers. The difference between the amount of the physicalsolid RI additive present in one of the resin layers and the amount ofphysical solid RI additive present in another layer, including, forexample, an adjacent layer, can be at least about 2, at least about 5,at least about 8, at least about 10 phr and/or not more than about 30,not more than about 25, or not more than about 20 phr, or it can be inthe range of from about 2 to about 30, about 5 to about 25, or about 10to about 20 phr. According to some embodiments, at least one of thelayers can include at least about 1, at least about 5, at least about10, at least about 15 phr and/or not more than about 60, not more thanabout 55, not more than about 50, not more than about 45 phr of thephysical solid RI additive, or the physical solid RI additive can bepresent in an amount in the range of from about 1 to about 60, about 10to about 50, or about 15 to about 45 phr. In some embodiments, thephysical solid RI additive can be present in one or more layers in anamount of at least about 5, at least about 10, at least about 15, atleast about 20 phr and/or not more than about 60, not more than about55, not more than about 50 phr, or in an amount in the range of fromabout 5 to about 60, about 15 to about 55, or about 20 to about 50 phr.

When the multilayer interlayer comprises three or more resin layers andthe solid RI additive is a solid high RI additive, the inner, or core,layer or layers can include higher amounts of the physical solid RIadditive than the outer, or skin, layers. However, if the solid RIadditive is a solid RI lowering additive, the outer skin layers mayinclude higher amounts of the solid RI additive than the inner corelayer. The core layer can include at least about 30, at least about 40,at least about 50, at least about 60, at least about 70, or at leastabout 80 percent of the total amount of physical solid RI additivepresent in the interlayer.

When the solid RI additive is a reactive solid RI additive, it may bereacted with at least one poly(vinyl acetal) resin such that at least aportion of the additive is incorporated into the polymer chain. Thereactive RI additive can be an aromatic additive and can comprise, insome embodiments, phthalic anhydrides and phenylalkoxysilanes including,for example, diphenyldimethoxysilane.

In some embodiments, the reactive RI additive may be present in onelayer of a multilayer interlayer in a higher amount than it is presentin one or more other layers of the interlayer. In some embodiments, itmay be absent, or substantially absent, from one or more resin layers.For example, when the interlayer is a multilayer interlayer including atleast three resin layers, the inner core layer may include at leastabout 0.5, at least about 1, at least about 1.5, at least about 2, atleast about 2.5, at least about 3 and/or not more than about 50, notmore than about 30, not more than about 20, not more than about 15, notmore than about 12, not more than about 10, or not more than about 8 phrof one or more reactive solid RI additives, or an amount in the range offrom about 0.5 to about 20, about 1 to about 12, or about 2 to about 8phr. The outer skin layer or layers may include not more than about 10,not more than about 5, not more than about 2, not more than about 1, ornot more than about 0.5 phr of the reactive solid RI additive. The corelayer can include at least about 65, at least about 75, at least about85, at least about 95, or at least about 99 percent of the total amountof the reactive RI additive present in the interlayer.

When a solid RI additive is used as an RI balancing agent in amultilayer interlayer, the interlayer can include at least one resinlayer having a first poly(vinyl acetal) resin and another resin layercomprising a second poly(vinyl acetal) resin, wherein the differencebetween the residual hydroxyl content of the first poly(vinyl acetal)resin and the second poly(vinyl acetal) resin is at least 2 weightpercent. At least one of the resin layers can include the high RIadditive in an amount sufficient so that the absolute value of thedifference between the refractive index of the first resin layer and therefractive index of the second resin layer is not more than 0.010. Insome embodiments when the interlayer includes at least three resinlayers, the innermost resin layer can have a higher refractive index,while in other embodiments, the refractive index of one or both of theouter resin layers may be higher.

When a solid RI additive is included in a resin layer comprising thepoly(vinyl acetal) resin having the lower residual hydroxyl content, theresin layer can have a glass transition temperature of not more than 25,not more than about 20, not more than about 15, not more than about 10,not more than about 5, not more than about 0, not more than about −5, ornot more than about −10° C., and a refractive index of at least about1.465, at least about 1.470, at least about 1.475, at least about 1.480,at least about 1.485, at least about 1.495, or at least about 1.500,each measured as described previously. The plasticizer content of thislayer, in some embodiments, can be at least about 50, at least about 55,at least about 60, at least about 65 phr and/or not more than about 120,not more than about 110, not more than about 90, not more than about 85,not more than about 80, or not more than about 75 phr, or in the rangeof from about 50 to about 120, about 55 to about 110, about 60 to about90, about 65 to about 75 phr.

When the solid RI additive is present in the resin layer that comprisesthe poly(vinyl acetal) resin having a higher residual hydroxyl content,the layer can have a glass transition temperature of at least about 26,at least about 30, at least about 33, or at least about 35° C. In someembodiments, the layer can have a refractive index of at least about1.470, at least about 1.475, at least about 1.480, at least about 1.485,at least about 1.490, at least about 1.500, at least about 1.510. Theplasticizer content of this layer, according to some embodiments, can beless than 50 phr, not more than about 45 phr, not more than about 40phr, not more than about 30, or not more than about 20 phr.

Resin compositions, layers, and interlayers formulated according tovarious embodiments of the present invention to include at least twopoly(vinyl acetal) resins and an RI balancing agent can exhibit enhancedoptical properties without sacrificing other properties such as impactresistance and acoustic performance. As discussed above, due todifferences in properties or composition of the resins, such as, forexample, residual hydroxyl content, residual acetate content, oraldehyde residues, identical blends of the same resins formulatedwithout the RI balancing agent may provide compositions, layers, andinterlayers with reduced optical performance.

Clarity is one parameter used to describe the optical performance ofcompositions, layers, and interlayers described herein and may bedetermined by measuring haze value or percent. Haze value represents thequantification of light scattered by a sample in contrast to theincident light. In some embodiments, the resin blends, layers, andinterlayers described herein may have a haze value of less than 5percent, less than about 4 percent, less than about 3 percent, less thanabout 2 percent, less than about 1, or less than about 0.5 percent, asmeasured in accordance with ASTM D1003-13—Procedure B using IlluminantC, at an observer angle of 2 degrees. The test is performed with aspectrophotometer, such as a Hunterlab UltraScan XE instrument(commercially available from Hunter Associates, Reston, Va.), on apolymer sample having a thickness of 0.76 mm, which has been laminatedbetween two sheets of clear glass each having a thickness of 2.3 mm(commercially available from Pittsburgh Glass Works of Pennsylvania).

Additionally, the resin layers and interlayers described herein may havea mottle value of not more than 3, not more than 2, or not more than 1.Mottle is another measure of optical quality, which is detected as atexture or graininess. Mottle is a visual defect if the level is toohigh or too severe, thereby causing objectionable visual appearance.Mottle is assessed and categorized by a side-by-side qualitativecomparison of shadowgraph projections for a test laminate with a set ofstandard laminate shadowgraphs that represent a series, or scale, ofmottle values ranging from 1 to 4, with 1 representing a standard of lowmottle (i.e., a low number of disruptions) and 4 representing a standardof high mottle (i.e., a high number of disruptions). High mottle isgenerally considered objectionable, particularly in automotive andarchitectural applications. Optionally, a model laminate having a singlelayer interlayer with zero mottle (no mottle) is used to facilitate theevaluation in a test laminate that has a mottle rating lower than thescale of the standard set, such as lower than a rating of 1. A testlaminate that shows a shadowgraph projection similar to that of azero-mottle laminate is assessed to have a mottle rating of zero. Thetest laminate is prepared with two sheets of clear glass each having athickness of 2.3 mm (commercially available from Pittsburgh Glass Worksof Pennsylvania) and an interlayer. The interlayer typically has arandom rough surface R_(z) of about 35 to 40 microns and thickness of0.76 to 0.86 mm.

The mottle values provided herein were determined using a Clear MottleAnalyzer (CMA) that includes a xenon arc lamp, a sample holder, aprojection screen, and a digital camera. The xenon arc lamp is used toproject a shadowgraph of a laminated sample onto the screen and thecamera is configured to capture an image of the resulting shadowgraph.The image is then digitally analyzed using computer imaging software andcompared to images of previously-captured standard samples to determinethe mottle of the sample. A method of measuring mottle using a CMA isdescribed in detail in U.S. Patent Application Publication No. US2012-0133764.

Another parameter used to determine the optical performance istransparency, or percent visual transmittance (% T_(vis)), which ismeasured using a spectrophotometer, such as a HunterLab UltraScan EX, inaccordance with ASTM D1003, Procedure B using Illuminant C at anobserver angle of 2°. The values provided herein were obtained byanalyzing a glass laminate samples having an interlayer thickness ofabout 0.76 mm and a clear glass thickness of 2.3 mm (commerciallyavailable from Pittsburgh Glass Works of Pennsylvania). In someembodiments, the resin layers and interlayers of the present inventioncan have a percent visual transmittance of at least about 70, at leastabout 75, at least about 80, at least about 81, at least about 82, atleast about 83, at least about 84, at least about 85, at least about85.5, at least about 86, at least about 86.5, at least about 87, atleast about 87.5, at least about 88, or at least about 88.5 percent.More specifically, the resin layers and interlayers of the presentinvention have a %T_(vis) of greater than 85 for the interlayerscontaining only additives of ACAs, UV stabilizers, and antioxidant, orgreater than 80% for the interlayers containing additional additivessuch as pigments, IR absorbers or blockers as mentioned above. Polymerinterlayers containing high levels of pigments and/or dyes may havelower % T_(vis) values as desired, such as in mass pigmented or coloredpolymer interlayers.

In addition to exhibiting one or more optical properties within theranges above, the resin layers and interlayers described herein may alsoexhibit acoustic properties within a desirable range. In someembodiments, as discussed above, at least a portion of a resin layer orinterlayer may have a glass transition temperature of not more than 25,not more than about 20, not more than about 15, not more than about 10,not more than about 5, not more than about 0, not more than about −5, ornot more than about −10° C., which may facilitate acoustic performanceof the layer or interlayer. At the same time, at least a portion of thelayer or interlayer may have a glass transition temperature of at leastabout 26, at least about 30, at least about 35° C., which may facilitateimpact resistance properties and strength.

In some embodiments, a resin layer or interlayer according to thepresent invention may have a tan delta value of at least about 0.70. Tandelta is the ratio of the loss modulus (G″) in Pascals to the storagemodulus (G′) in Pascals of a specimen measured by Dynamic MechanicalThermal Analysis (DMTA). The DMTA is performed with an oscillationfrequency of 1 Hz under shear mode and a temperature sweep rate of 3°C./min. The peak value of the G″/G′ curve at the glass transitiontemperature is the tan delta value. Resin layers or interlayers asdescribed according to various embodiment herein can have a tan delta ofat least about 1.0, at least about 1.05, at least about 1.10, at leastabout 1.25, at least about 1.50, at least about 1.75, at least about2.0, or at least about 2.25.

Additionally, the resin layers and interlayers can have a damping lossfactor, or loss factor, of at least about 0.10, at least about 0.15, atleast about 0.17, at least about 0.20, at least about 0.25, at leastabout 0.27, at least about 0.30, at least about 0.33, or at least about0.35. Loss factor is measured by Mechanical Impedance Measurement asdescribed in ISO Standard 16940. A polymer sample is laminated betweentwo sheets of clear glass, each having a thickness of 2.3 mm, and isprepared to have a width of 25 mm and a length of 300 mm. The laminatedsample is then excited at the center point using a vibration shaker,commercially available from Brüel and Kjær (Nærum, Netherlands) and animpedance head (Brüel and Kjær) is used to measure the force required toexcite the bar to vibrate and the velocity of the vibration. Theresultant transfer function is recorded on a National Instrument dataacquisition and analysis system and the loss factor at the firstvibration mode is calculated using the half power method. In someembodiments, when the RI balancing agent is a high RI plasticizer, thelayer or interlayer may have a loss factor greater than 0.25, greaterthan 0.27, greater than 0.30, or greater than 0.35 at 20° C., while, inother embodiments, when the RI balancing agent is a solid RI additive orresidues of at least one high RI aldehyde, the layer or interlayer mayhave a loss factor of at least about 0.10, at least about 0.15, at leastabout 0.20, at least about 0.25, or at least about 0.30° C. 20° C.

Similar to the resin blend of two distinct resins of the firstpoly(vinyl acetal) resin and the second poly(vinyl acetal) resin,blending two or more distinct resin layers or interlayers can oftenresult in the new resin layer(s) or interlayer(s) having unexpectedproperties and performance attributes. For example, a resin layer orinterlayer having lower residual hydroxyl content and lower glasstransition temperature may be blended with another resin layer orinterlayer having higher residual hydroxyl content and higher glasstransition temperature, resulting a new resin layer or interlayer havingsoft domains of lower glass transition temperature, which enhances itsacoustic performance, and stiff domains of higher glass transitiontemperature, which imparts enhanced processability, strength, and impactresistance to the resin layer or interlayer. Other example includesblending a single sheet interlayer and multilayer interlayer, blendingtwo multilayer interlayers, or blending one multilayer interlayer into aresin layer of another multilayer interlayer. In essence, the effectarising from blending two materials can also be achieved from blendingtwo or more resins, plasticizers, and other additives according to thecontents of the materials. As used herein, a “blend resin material” or“blend material” refers to the resin composition, resin layer orinterlayer to be blended into another resin composition, resin layer orinterlayer. In blending two resin layers or two interlayers, at leastone of the two materials to be blended can include the resin layer orinterlayer of the present invention. In other embodiments, bothmaterials can include the resin layers or interlayers of the presentinvention.

According to some embodiments, at least a portion of the resincompositions, layers, or interlayers described herein may compriseanother resins, layers, or interlayers. In some embodiments, at leastabout 0.5, at least about 1, at least about 5, at least about 10, atleast about 15, at least about 20, at least about 25, at least about 30,or at least about 50 percent of the total amount of resin in acomposition, layer, or interlayer can originate from a blend resinmaterial.

Often, when the type and/or amount of resins and plasticizers in theblend resin material differ substantially from the type and/or amount ofthe resin or plasticizer being produced, and into which the blend resinmaterial is being added, the optical performance, as determined by theclarity or haze, of the resulting resin composition, layer, orinterlayer that includes the blend resin material may be adverselyimpacted. According to embodiments of the present invention, resinlayers and interlayers that include higher levels of blend resinmaterial can be produced by utilizing one or more of the RI balancingagents discussed above.

When the RI balancing agent includes a high RI plasticizer, higheramounts of blend resin materials can be added to a process for producinga resin composition, layer, or interlayer described herein withoutreducing the clarity or increasing the haze of the final composition,layer, or interlayer. In some embodiments, the composition that includesblend materials can include a first poly(vinyl acetal) resin and asecond poly(vinyl acetal) resin, wherein one of the resins has aresidual hydroxyl content that can be at least 2 weight percent lowerthan the residual hydroxyl content of the other resin. Such acomposition may further include at least one high RI plasticizer havinga refractive index of 1.460, and, in some embodiments, more than 3percent of the combined amount of the first and second poly(vinylacetal) resins present in the composition, layer, or interlayer may haveoriginated from a blend composition, layer, or interlayer. Despite thedifference in residual hydroxyl contents of the first and secondpoly(vinyl acetal) resins, the composition that includes more than 0.5weight percent of blend resin materials may have a haze value of notmore than about 5, not more than about 4, not more than about 3, notmore than about 2, or not more than about 1, or not more than about 0.5.

The high RI plasticizer used as an RI balancing agent with blend resincompositions can have a refractive index within one or more of theranges described previously. The high RI plasticizer may be added duringproduction of the composition, layer, or interlayer along with the blendmaterial and/or at least a portion of the high RI plasticizer may bepresent in the blend resin material added to the process. Additionally,one or more other plasticizers may also be present in the resin materialbeing blended and/or in the resin composition, layer, or interlayerbeing produced, including, for example, those having a refractive indexless than about 1.450, less than about 1.445, or less than about 1.442,measured as described previously. In some embodiments, one or moreadditional high RI plasticizers may also be present in the blendmaterial and/or in the resin composition, layer, or interlayer intowhich the materials are being blended.

The resin composition that includes blended resin material as describedabove can be used to form layers and interlayers according to variousembodiments of the present invention. For example, the resin compositionincluding a blend resin material can be used to form a single monolithicinterlayer, or it may be used to form one or more layers of a multilayerinterlayer. When used in various layers and interlayers, additionalplasticizer may be added such that the total amount of plasticizerpresent in the resin layer or interlayer can be within the rangedescribed previously. Similarly, the glass transition temperature andrefractive indices of resin layers and interlayers formed from acomposition that includes a blend resin material may also be within theranges provided above. Additionally, resin layers and interlayers formedfrom a composition that includes blended materials may also exhibitacoustic properties as described previously and may be included in anyof the applications described below.

According to some embodiments, at least a portion of the resincompositions, layers, or interlayers described herein may comprise oneor more recycled resin materials, including, for example, recycledlayers or interlayers. As used herein, the term “recycled” means removedfrom and subsequently returned to a production line. Often, utilizingrecycled materials may adversely affect the optical performance of thefinal composition, layer, or interlayer, as determined by clarity orhaze, because of the different compositions and properties of thematerials being blended or combined. However, in some embodiments,layers or interlayers as described herein may include at least onerecycled resin material, while still exhibiting the same optical and/oracoustic properties as described herein. The type and/or amount ofrecycle resin material may fall within one or more of the rangesdescribed previously and the layer or interlayer may further include atleast one RI balancing agent. Additionally, the resin layers andinterlayers including recycled resin material may also have opticaland/or acoustic performance within one or more of the ranges describedbelow.

The resin compositions, layers, and interlayers described above may beproduced according to any suitable method. In various embodiments, themethod for producing these compositions, layers, and interlayers caninclude providing two or more poly(vinyl acetal) resins, blending atleast one resin with an RI balancing agent and, optionally, at least oneplasticizer or other additive, to form a blended composition, andforming a layer from the blended composition.

In some embodiments, the resins provided in the initial steps of themethod can be in the form of one or more poly(vinyl acetal) resins,while, in other embodiments, one or more resin precursors can also beprovided. In some embodiments, when two or more poly(vinyl acetal)resins are physically blended, the blending of the two resins cancomprise melt blending and may be performed at a temperature of at leastabout 140, at least about 150, at least about 180, at least about 200,at least about 250° C. In other embodiments, when the poly(vinyl acetal)resin components provided include resin precursors, the blending stepmay include reacting two or more aldehydes with a polyvinyl alcohol toprovide a single poly(vinyl acetal) resin having two or more aldehydemoieties. Additionally, a portion of the blending step can includeblending one or more of the resins with at least one plasticizer and/orwith one or more of the RI balancing agents described previously.

The resulting blended resins can then be formed into one or more resinlayers according to any suitable method. Exemplary methods of formingpolymer layers and interlayers can include, but are not limited to,solution casting, compression molding, injection molding, meltextrusion, melt blowing, and combinations thereof. Multilayerinterlayers including two or more resin layers may also be producedaccording to any suitable method such as, for example, co-extrusion,blown film, melt blowing, dip coating, solution coating, blade, paddle,air-knife, printing, powder coating, spray coating, and combinationsthereof. In various embodiments of the present invention, the layers orinterlayers may be formed by extrusion or co-extrusion. In an extrusionprocess, one or more thermoplastic polymers, plasticizers, and,optionally, at least one additive, including one or more RI balancingagents as described previously, can be pre-mixed and fed into anextrusion device. Other additives, such as ACAs, colorants, and UVinhibitors, which can be in liquid, powder, or pellet form, may also beused and may be mixed into the thermoplastic polymers or plasticizersprior to entering the extrusion device. These additives can beincorporated into the polymer resin and, by extension, the resultantpolymer sheet, thereby enhancing certain properties of the polymer layeror interlayer and its performance in the final multiple layer glasspanel or other end product.

In various embodiments, the thickness, or gauge, of the layers orinterlayers can be at least about 10, at least about 15, at least about20 mils and/or not more than about 100, not more than about 90, not morethan about 60, not more than about 50, or not more than about 35 mils,or it can be in the range of from about 10 to about 100, about 15 toabout 60, or about 20 to about 35 mils. In millimeters, the thickness ofthe polymer layers or interlayers can be at least about 0.25, at leastabout 0.38, at least about 0.51 mm and/or not more than about 2.54, notmore than about 2.29, not more than about 1.52, or not more than about0.89 mm, or in the range of from about 0.25 to about 2.54 mm, about 0.38to about 1.52 mm, or about 0.51 to about 0.89 mm. In some embodiments,the resin layers or interlayers can comprise flat polymer layers havingsubstantially the same thickness along the length, or longest dimension,and/or width, or second longest dimension, of the sheet, while, in otherembodiments, one or more layers of a multilayer interlayer, for example,can be wedge-shaped or can have a wedge-shaped profile, such that thethickness of the interlayer changes along the length and/or width of thesheet, such that one edge of the layer or interlayer has a thicknessgreater than the other. When the interlayer is a multilayer interlayer,at least one, at least two, or at least three of the layers of theinterlayer can be wedge-shaped. When the interlayer is a monolithicinterlayer, the polymer sheet can be flat or wedge shaped. Wedge-shapedinterlayers may be useful in, for example, heads-up-display (HUD) panelsin automotive and aircraft applications.

The resin compositions, layers, and interlayers according to embodimentsof the present invention may be utilized in a multiple layer panel thatcomprises a resin layer or interlayer and at least one rigid substrate.Any suitable rigid substrate may be used and in some embodiments may beselected from the group consisting of glass, polycarbonate, biaxiallyoriented PET, copolyesters, acrylic, and combinations thereof. When therigid substrate includes glass, the glass can be selected from the grouplisted previously. When the rigid substrate includes a polymericmaterial, the polymeric material may or may not include a hard coatsurface layer. In some embodiments, the multilayer panels include a pairof rigid substrates with the resin interlayer disposed therebetween. Thepanels can be used for a variety of end use applications, including, forexample, for automotive windshields and windows, aircraft windshieldsand windows, panels for various transportation applications such asmarine applications, rail applications, etc., structural architecturalpanels such as windows, doors, stairs, walkways, balusters, decorativearchitectural panels, weather-resistant panels, such as hurricane glassor tornado glass, ballistic panels, and other similar applications.

When laminating the resin layers or interlayers between two rigidsubstrates, such as glass, the process can include at least thefollowing steps: (1) assembly of the two substrates and the interlayer;(2) heating the assembly via an IR radiant or convective device for afirst, short period of time; (3) passing the assembly into a pressurenip roll for the first de-airing; (4) heating the assembly for a shortperiod of time to about 60° C. to about 120° C. to give the assemblyenough temporary adhesion to seal the edge of the interlayer; (5)passing the assembly into a second pressure nip roll to further seal theedge of the interlayer and allow further handling; and (6) autoclavingthe assembly at temperature between 135° C. and 150° C. and pressuresbetween 150 psig and 200 psig for about 30 to 90 minutes. Other methodsfor de-airing the interlayer-glass interface, as described according tosome embodiments in steps (2) through (5) above include vacuum bag andvacuum ring processes, and both may also be used to form interlayers ofthe present invention as described herein.

In some embodiments, the multiple layer panel may include at least onepolymer film disposed on the layer or interlayer, forming a multiplelayer panel referred to as a “bilayer.” In some embodiments, theinterlayer utilized in a bilayer may include a multilayer interlayer,while, in other embodiments, a monolithic interlayer may be used. Theuse of a polymer film in multiple layer panels as described herein mayenhance the optical character of the final panel, while also providingother performance improvements, such as infrared absorption. Polymerfilms differ from polymer layers or interlayers in that the films alonedo not provide the necessary penetration resistance and glass retentionproperties. The polymer film can also be thinner than the sheet, and mayhave a thickness in the range of from 0.001 to 0.25 mm. Poly(ethyleneterephthalate) (“PET”) is one example of a material used to form thepolymer film.

The following examples are intended to be illustrative of the presentinvention in order to teach one of ordinary skill in the art to make anduse the invention and are not intended to limit the scope of theinvention in any way.

EXAMPLES

The following Examples describe the preparation of several resincompositions, layers, and interlayers that include various poly(vinylacetal) reins. As described below, several tests performed on many ofthe compositions, layers, and interlayers were used to evaluate theacoustic and optical properties of several comparative and inventivematerials.

Example 1 Preparation of High Refractive Index Poly(vinyl acetal) Resins

Several comparative poly(vinyl acetal) resins, referred to asComparative Resins CR-1 through CR-12 in Table 2 below, were prepared byacetalizing polyvinyl alcohol with one or more aldehydes includingn-butyraldehyde (nBuCHO; RI=1.377), iso-butyraldehyde (iBuCHO;RI=1.374), and 2-ethylhexyl aldehyde (2EHCHO; RI=1.414). Thecompositions of the resulting resins were measured using either the ASTMD1396 or FT-IR/SEC method described in detail previously. The refractiveindex and glass transition temperature (T_(g)) of several of the resinswas also measured according to the methods described previously, and theresults are provided in Table 2, below.

TABLE 2 Properties of Several Comparative Poly(vinyl acetal) ResinsResidual Residual Residual Resin Residual Residual Polyvinyl PolyvinylPolyvinyl Refractive Hydroxyl Acetate nBuCHO iBuCHO 2EHCHO Index Resin(wt %) (wt %) (wt %) (wt %) (wt %) (nD25) CR-1 21 1 78 — — 1.491 CR-2 191 80 — — 1.490 CR-3 19 1 46 — 34 1.489 CR-4 16 1 83 — — 1.488 CR-5 15 139 — 45 1.487 CR-6 13 1 86 — — 1.486 CR-7 12 18 70 — — 1.481 CR-8 12 1276 — — nd CR-9 12 10 78 — — 1.483 CR-10 11 1 88 — — 1.485 CR-11 12 1 —88 — nd CR-12 13 1 — 86 — nd nd = not determined

Additionally, several poly(vinyl acetal) resins according to embodimentsof the present invention were also prepared in a similar manner. Theseinventive resins, referred to as Disclosed Resins DR-1 through DR-21 inTable 3, were formed by acetalizing polyvinyl alcohol with mixtures ofn-butyraldehyde and various high refractive index aldehydes, includingbenzaldehyde (BzCHO RI=1.545), cinnamaldehyde (CCHO; RI=1.620),4-chlorobenzaldehyde (4-CIBzCHO; RI=1.5850), 2-phenylpropionaldehyde(2PHPrCHO; RI=1.517), and hydrocinnamaldehyde (HCCHO; RI=1.523). Therefractive index of several of the Disclosed Resins was also determinedand the results are summarized in Table 3, below.

TABLE 3 Properties of Disclosed Resins Resin Residual Residual AldehydeHCCHO/ CCHO/ 2PhPrCHO/ BzCHO/ 4ClBzCHO/ Refractive Hydroxyl AcetateComponent BuCHO BuCHO BuCHO BuCHO BuCHO HCCHO/ Index Resin (wt %) (wt %)(wt %) (mol/mol) (mol/mol) (mol/mol) (mol/mol) (mol/mol) iBuCHO (nD25)DR-1 11 1 88  5/95 — — — — — 1.496 DR-2 11 1 88 10/90 — — — — — 1.500DR-3 11 1 88 15/85 — — — — — 1.504 DR-4 11 1 88 20/80 — — — — — 1.510DR-5 11 1 88 25/75 — — — — — 1.511 DR-6 11 1 88 50/50 — — — — — 1.528DR-7 11 1 88 100/0  — — — — — 1.552 DR-8 19 1 80 10/90 — — — — — nd DR-919 1 80 25/75 — — — — — nd DR-10 19 1 80 50/50 — — — — — nd DR-11 19 180 100/0  — — — — — nd DR-12 12 18 70 25/75 — — — — — nd DR-13 12 10 7825/75 — — — — — nd DR-14 17 1 82 — 25/75 — — — — 1.507 DR-15 15 1 84 — —25/75 — — — 1.505 DR-16 14 1 85 — — 25/75 — — — 1.503 DR-17 18 1 81 — —— 25/75 — — 1.507 DR-18 14 1 85 — — — 25/75 — — 1.501 DR-19 20 1 79 — —— — 25/75 — 1.507 DR-20 14 1 85 — — — — 25/75 — 1.509 DR-21 11 1 88 — —— — — 25/75 nd nd = not determined

As shown in Tables 2 and 3, above, polyvinyl acetal resins comprisingresidues of at least one high refractive index aldehyde, including thoselisted above, tend to exhibit higher refractive indices than thosecomprising residues of aldehydes such as n-butyraldehyde,iso-butyraldehyde, and 2-ethylhexyl aldehyde.

Example 2 Preparation of High Refractive Index Resin Interlayers

Several Comparative and Disclosed Interlayers were formed by mixing andmelt blending several of the Comparative Resins listed in Table 2 andseveral of the Disclosed Resins listed in Table 3 above, with varyingamounts of the plasticizer triethylene glycol bis(2-ethylhexanoate)(3GEH). The composition, refractive index, and glass transitiontemperature of each of the resulting interlayers, referred to asComparative Interlayers CL-1 through CL-14 and Disclosed InterlayersDL-1 through DL-26, were measured as described previously, and theresults are respectively summarized in Tables 4 and 5, below.

TABLE 4 Properties of Several Comparative Interlayers RefractivePlasticizer Index T_(g) Interlayer Resin (phr) (nD25) (° C.) CL-1 CR-134 1.478 36 CL-2 CR-2 38 1.477 30 CL-3 CR-3 38 1.475 28 CL-4 CR-4 501.472 17 CL-5 CR-4 30 1.477 30 CL-6 CR-5 75 1.468 6 CL-7 CR-6 75 1.467 2CL-8 CR-7 75 1.464 −4 CL-9 CR-8 75 1.466 −3  CL-10 CR-9 75 1.465 −3 CL-11  CR-10 75 1.466 −2  CL-12  CR-10 50 1.47  12  CL-13  CR-11 75 ndnd  CL-14  CR-12 75 nd nd nd = not determined

TABLE 5 Properties of Several Disclosed Interlayers Sheet PlasticizerRefractive content Index T_(g) Interlayaer Resin (phr) (nD25) (° C.)DL-1  DR-1  75 1.473 1 DL-2  DR-1  50 1.479 12 DL-3  DR-2  75 1.475 0DL-4  DR-3  75 1.477 0 DL-5  DR-4  75 1.480 1 DL-6  DR-5  75 1.482 1DL-7  DR-6  75 1.490 2 DL-8  DR-7  75 1.506 3 DL-9  DR-14 75 1.480 12DL-10 DR-15 75 1.478 11 DL-11 DR-16 75 1.477 7 DL-12 DR-17 75 1.480 22DL-13 DR-18 75 1.476 12 DL-14 DR-19 75 1.480 17 DL-15 DR-20 75 1.479 12DL-16 DR-12 75 nd nd DL-17 DR-13 75 nd nd DL-18 DR-21 75 nd nd DL-19DR-8  38 1.477 30 DL-20 DR-9  38 1.487 nd DL-21 DR-10 38 1.501 nd DL-22DR-11 38 1.525 nd DL-23 DR-5  38 nd nd DL-24 DR-5  50 1.488 nd DL-25DR-5  60 1.484 2 DL-26 DR-7  38 nd nd nd = not determined

As shown in Tables 4 and 5, above, Disclosed Interlayers utilizinghigher refractive index Disclosed Resins from Table 3 exhibit higherrefractive indices than Comparative Interlayers formulated with lowerrefractive index resins, such as the Comparative Resins listed in Table2. Additionally, as shown by comparison of Disclosed Interlayers DL-1and DL-2 and DL-6 and DL-23 through DL-25, the amount of plasticizerused to form an interlayer affects both the glass transition temperatureand refractive index of the layer, although not necessarily to the sameextent for all resins. For example, as shown by the comparison of DL-1(75 phr 3GEH; Disclosed Resin 1) and DL-2 (50 phr 3GEH; Disclosed Resin1), reducing the amount of plasticizer by about 33 percent increases theglass transition temperature of the interlayer by 11° C. (from 1° C. to12° C.), but only increases the refractive index by 0.006 (from 1.473 to1.479). However, as shown by the comparison of DL-25 (60 phr 3GEH;Disclosed Resin 5) and DL-6 (75 phr of 3GEH; Disclosed Resin 5),reducing the plasticizer content in layers formed by this resinincreases the glass transition temperature by only 1° C. (from 1° C. to2° C.), while increasing the refractive index by 0.004 (from 1.484 to1.488).

Example 3 Preparation of Interlayers using High Refractive Index Resins

Several of the Comparative and Disclosed Interlayers formed in Example 2and respectively summarized in Tables 4 and 5, above, were used tocreate several Comparative and Disclosed Multilayer Interlayers. Eachmultilayer interlayer included a pair of outer “skin” layers, having atotal thickness of 28 mils, sandwiching an inner “core” layer having athickness of 5 mils, usually formed of a resin having a lower residualhydroxyl content. The composition and several properties of theinterlayers including refractive index, glass transition temperature,mottle, and loss factor, were measured as described above, and theresults for the Comparative Multilayer Interlayers (CI-1 to CI-16) andDisclosed Multilayer Interlayers (DI-1 to DI-29) are summarized inTables 6 and 7, below.

TABLE 6 Properties of Several Comparative Multilayer Interlayers ΔRefractive Refractive Loss Index Index of Factor Resin Layer T_(g) (°C.) Refractive Index (Skin- Interlayer at Interlayer Skin 1 Core Skin 2Skin 1 Core Skin 2 Skin 1 Core Skin 2 Core) (nD25) Mottle 20° C. CI-1CL-2 CL-7 CL-2 30 2 30 1.477 1.467 1.477 0.010 1.475 4 0.29 CI-2 CL-2CL-11 CL-2 30 −2 30 1.477 1.466 1.477 0.011 1.475 5 0.33 CI-3 CL-2 CL-8CL-2 30 −4 30 1.477 1.464 1.477 0.013 1.475 5 nd CI-4 CL-1 CL-9 CL-1 36−3 36 1.478 1.466 1.478 0.012 1.477 5 nd CI-5 CL-1 CL-8 CL-1 36 −4 361.478 1.464 1.478 0.014 nd 5 0.36 CI-6 CL-2 CL-9 CL-2 30 −3 30 1.4771.466 1.477 0.011 nd 5 nd CI-7 CL-1 CL-11 CL-1 36 −2 36 1.478 1.4661.478 0.012 1.477 5 0.35 CI-8 CL-2 CL-10 CL-2 30 −3 30 1.477 1.465 1.4770.012 nd 5 0.31 CI-9 CL-1 CL-7 CL-1 36 2 36 1.478 1.467 1.478 0.011 nd 5nd CI-10 CL-1 CL-10 CL-1 36 −3 36 1.478 1.465 1.478 0.013 nd 5 nd CI-11CL-2 CL-13 CL-2 30 nd 30 nd nd nd nd nd >5 nd CI-12 CL-2 CL-14 CL-2 30nd 30 nd nd nd nd nd >5 nd CI-13 CL-1 CL-13 CL-1 36 nd 36 nd nd nd ndnd >5 nd CI-14 CL-1 CL-14 CL-1 36 nd 36 nd nd nd nd nd >5 nd CI-15 CL-2DL-7 CL-2 30 2 30 1.477 1.490 1.477 −0.013 1.479 >5 nd CI-16 CL-2 DL-8CL-2 30 3 30 1.477 1.506 1.477 −0.029 1.481 >5 nd nd = not determined

TABLE 7 Properties of Some Disclosed Multilayer Interlayers Δ RefractiveRefractive Index Index Refractive Resin Layer T_(g) (° C.) (nD25) (Skin-Index of Interlayer Skin 1 Core Skin 2 Skin 1 Core Skin 2 Skin 1 CoreSkin 2 Core) Interlayer Mottle DI-1 CL-2 DL-1 CL-2 30 1 30 1.477 1.4731.477 0.004 1.476 1 DI-2 CL-2 DL-4 CL-2 30 0 30 1.477 1.477 1.477 0.0001.477 1 DI-3 CL-5 DL-6 CL-5 30 1 30 1.477 1.482 1.477 −0.005 1.478 ndDI-4 CL-2 DL-6 CL-2 30 1 30 1.477 1.482 1.477 −0.005 nd <1 DI-5 CL-1DL-6 CL-1 36 1 36 1.478 1.482 1.478 −0.004 nd <1 DI-6 CL-2 DL-3 CL-2 300 30 1.477 1.475 1.477 0.002 nd <1 DI-7 CL-2 DL-5 CL-2 30 1 30 1.4771.480 1.477 −0.003 nd <1 DI-8 CL-2 DL-6 CL-1 30 1 36 1.477 1.482 1.478−0.005 nd <1 DI-9 CL-2 DL-6 CL-5 30 1 30 1.477 1.482 1.477 −0.005 nd <1DI-10 CL-2 DL-16 CL-2 30 nd 30 1.477 nd 1.477 nd nd <1 DI-11 CL-2 DL-17CL-2 30 nd 30 1.477 nd 1.477 nd nd <1 DI-12 CL-1 DL-16 CL-1 36 nd 361.478 nd 1.478 nd nd <1 DI-13 CL-1 DL-17 CL-1 36 nd 36 1.478 nd 1.478 ndnd <1 DI-14 CL-2 DL-18 CL-2 30 nd 30 1.477 nd 1.477 nd nd <1 DI-15 CL-1DL-18 CL-1 36 nd 36 1.478 nd 1.478 nd nd <1 DI-16 DL-19 DL-24 DL-19 30 130 1.477 1.488 1.477 −0.005 1.478 <1 DI-17 CL-2 DL-9 CL-2 30 12 30 1.4771.480 1.477 −0.003 nd <1 DI-18 CL-2 DL-10 CL-2 30 11 30 1.477 1.4781.477 −0.001 nd <1 DI-19 CL-2 DL-11 CL-2 30 7 30 1.477 1.477 1.477 0.000nd <1 DI-20 CL-2 DL-12 CL-2 30 22 30 1.477 1.480 1.477 −0.003 nd <1DI-21 CL-2 DL-13 CL-2 30 12 30 1.477 1.476 1.477 0.001 nd <1 DI-22 CL-2DL-14 CL-2 30 17 30 1.477 1.480 1.477 −0.003 nd <1 DI-23 CL-2 DL-15 CL-230 12 30 1.477 1.479 1.477 −0.002 nd <1 DI-24 DL-20 DL-7 DL-20 nd 2 nd1.487 1.490 1.487 −0.003 nd <1 DI-25 DL-21 DL-7 DL-21 nd 2 nd 1.5011.490 1.501 −0.011 nd >5 DI-26 DL-22 DL-7 DL-22 nd 2 nd 1.525 1.4901.525 −0.035 nd >5 DI-27 DL-20 DL-8 DL-20 nd 3 nd 1.487 1.506 1.487−0.009 nd 3 DI-28 DL-21 DL-8 DL-21 nd 3 nd 1.501 1.506 1.501 −0.005 nd<1 DI-29 DL-22 DL-8 DL-22 nd 3 nd 1.525 1.506 1.525 −0.019 nd >5 nd =not determined

As shown in Table 6, above, interlayers formed from skin and core layershaving refractive index differences of 0.010 or more exhibited opticaldefects, as indicated by the mottle values greater than 5. As shown inTable 7, however, interlayers formed from skin and core layers havingrefractive index differences of less than 0.010 exhibited low mottlevalues of 1 or less. Additionally, as shown in Table 7, such low mottlevalues were achievable by interlayers having a core layer with a higheror lower refractive index than the skin layer, as long as the absolutevalue of the difference between the refractive indices of adjacentlayers was less than 0.010. Also as shown in Table 7, interlayers formedfrom skin and core layers both having high RI aldehyde residues andhaving refractive index differences of greater than 0.010 exhibited highmottle values of 5 or greater.

Example 4 Stability of Multilayer Interlayers

Two Comparative Multilayer Interlayers, CI-2 and CI-7, and two DisclosedMultilayer Interlayers, DI-4 and DI-5, prepared as described in Examples1-3 above, were tested to determine the relative stability of theinterlayers over time. Net plasticizer migration, which was measured bycomparing the glass transition temperatures of each layer at an initialtime (t=0) and after the layers have achieved equilibrium. The resultsare summarized in Table 8, below.

TABLE 8 Net Plasticizer Migration and Properties of ExemplaryComparative and Disclosed Interlayers T_(g) at Δ T_(g) at t = 0Equilibrium Δ T_(g) Refractive (° C.) (° C.) (° C.) Index T_(g) T_(g)T_(g) T_(g) Δ T_(g) Δ T_(g) (Skin- Interlayer Skin Core Skin Core SkinCore Core) Mottle CI-2 36 4.2 36 4.6 0.0 0.4 0.011 >5 DI-4 36 1.4 36.41.4 0.4 0.0 −0.005 <1 CI-7 42.5 2.2 42.5 1.4 0.0 −0.8 0.012 >5 DI-5 40.90.2 41.7 −1.8 0.8 −2.0 −0.004 <1

Disclosed Interlayer DI-4 exhibited minimal changes in the glasstransition temperature of both the skin and core layers of theinterlayer at equilibrium. This indicates a minor amount of plasticizermigration between the skin and core layers of each of Interlayers CI-2,CI-7, and DI-4. Although Comparative Interlayers CI-2 and CI-7 may berelatively stable, both exhibited a mottle value greater than 5, whichwould be unacceptable for most optical applications. In contrast, themottle value exhibited by Disclosed Interlayer DI-4 was less than 1.

The slight decrease in glass transition temperature exhibited byDisclosed Interlayer DI-5 at equilibrium indicated that a small amountof plasticizer migrated from the skin layer to the core layer. Suchmigration could be alleviated by utilizing a smaller amount ofplasticizer in the skin layer or a larger amount in the core. Even so,the refractive index of the core layer and the skin layer of DisclosedInterlayer DI-5 differed by only 0.004 and, as a result, the interlayeralso exhibited a mottle value less than 1.

Example 5 Blended Poly(vinyl acetal) Resins

Several Comparative and Disclosed Resins, prepared as described inExample 1 above, were mixed and melt-blended together with 38 phr of3GEH plasticizer to form Comparative Blended Layers CBL-16 and CBL-17and Disclosed Blended Layers DBL-27 and DBL-28. Comparative Resin LayerCL-2 is listed in Table CL-15 was formulated with Comparative ResinCR-10 and 38 phr of 3GEH, while Disclosed Resin Layers DL-27 and DL-28were formulated with Disclosed Resins DR-3 and DR-5, respectively, and38 phr of 3GEH. The haze and percent visual transmittance (T_(vis)) foreach blended resin interlayer were measured, along with the haze andpercent visual transmittance. The results are provided in Table 9,below.

TABLE 9 Haze and Percent Visual Transmittance of Several Resin Layersposition Plasticizer Property CR-2 CR-10 DR-3 DR-5 content HazeInterlayer (wt %) (wt %) (wt %) (wt %) (phr) (%) % T_(vis) CL-2 100 — —— 38 0.5 87.7 CL-15 — 100 — — 38 0.5 87.8 CBL-16 96 4 — — 38 2.1 84.3CBL-17 89 11 — — 38 14.7 80.2 DBL-27 96 — 4 — 38 0.8 87.8 DBL-28 89 — —11 38 0.6 87.8 DL-27 — — 100 — 38 0.5 87.7 DL-28 — — — 100 38 0.5 87.8

As shown in Table 9 above, Comparative Blended Interlayers CBL-16 andCBL-17, which were formed from a blend of Comparative Resins CR-2 andCR-10, exhibited high haze values and lower percent visual transmittancethan single resin layers of Comparative Resin CR-2 (Comparative LayerCL-2) or CR-10 (Comparative Interlayer CL-15). In contrast, DisclosedBlended Interlayers DBL-27 and DBL-28, which were formed from a blend ofComparative Resin CR-2 and a high refractive index Disclosed Resin(Resin DR-3 in Layer DBL-27 or Resin DR-5 in Layer DBL-28), exhibitedsubstantially the same haze and percent visual transmittance asComparative Interlayer CL-2, which was formulated with Comparative ResinCR-2 alone. Thus, addition of inventive high refractive index resins toa comparative interlayer does not reduce the optical quality of theresulting interlayer.

Example 6 Preparation of Interlayers having High Refractive IndexAdditives

Several poly(vinyl acetal) resins were prepared by acetalizing polyvinylalcohol with n-butyraldehyde. The resins, which had different residualhydroxyl contents, were melt blended with varying amounts of a 3GEHplasticizer and used to form various layers of multilayer interlayers.Each interlayer had an inner “core” layer having a thickness of 5 milssandwiched between two outer “skin” layers, each having a thickness of14 mils. The poly(vinyl butyral) resin used to form the core layers hada hydroxyl content of 11 weight percent and the resin used for the skinlayers had a hydroxyl content of 19 weight percent. Both resins had aresidual acetate content of about 2 weight percent.

Comparative Interlayers CI-17 through CI-19 were formed with resinlayers plasticized with 3GEH, which was present in varying amounts inthe core and skin layers. In addition to the 3GEH, Disclosed InterlayersDI-30 through DI-38 also included varying amounts of two different highrefractive index additives, Benzoflex™ 2-45 (diethyleneglycoldibenzoate; commercially available from Eastman Chemical Company,Kingsport, Tenn.) (Additive A-1), which had a melting point of 28° C.and a refractive index of 1.542; and Benzoflex™ 352 (1,4-cyclohexanedimethanol dibenzoate; commercially available from Eastman ChemicalCompany) (Additive A-2), which had a melting point of 118° C. and arefractive index of 1.554. The refractive index and glass transitiontemperatures of each of the layers of Comparative Interlayers CI-17through CI-19 and Disclosed Interlayers DI-30 through DI-38 weremeasured and the results are summarized in Table 10 below.

TABLE 10 Properties of Several Comparative and Disclosed InterlayersSkin Layers High Core Layer RI High RI Δ Plasticizer High RI AdditivePlasticizer High RI Additive Refractive Content (P) Additive (A) TotalA:P Tg Content (P) Additive (A) Total A:P Tg Index Interlayer (phr) Type(phr) A + P Ratio RI (° C.) (phr) Type (phr) A + P Ratio RI (° C.)(Skin-Core) CI-17 40 — — — 1.476 30 65.0 — — — 1.467 2.9 0.008 CI-18 40— — — 1.476 30 75.0 — — — 1.466 −2.0 0.010 CI-19 40 — — — 1.476 30 85.0— — — 1.465 −3.1 0.011 DI-30 20 A-1 20 40 1.0 1.492 29 32.5 A-1 32.5 651.0 1.488 4.2 0.004 DI-31 20 A-1 20 40 1.0 1.492 29 37.5 A-1 37.5 75 1.01.488 −0.6 0.004 DI-32 20 A-1 20 40 1.0 1.489 29 42.5 A-1 42.5 85 1.01.488 −3.3 0.004 DI-33 17.2 A-1 22.8 40 1.3 1.496 30 22.8 A-1 42.2 651.9 1.494 5.2 0.002 DI-34 17.2 A-1 22.8 40 1.3 1.496 30 26.2 A-1 48.8 751.9 1.494 2.4 0.002 DI-35 17.2 A-1 22.8 40 1.3 1.496 30 29.8 A-1 55.2 851.9 1.494 −2.1 0.002 DI-36 20 A-2 20 40 1.0 1.493 34 27.5 A-2 27.5 551.0 1.490 15.9 0.003 DI-37 20 A-2 20 40 1.0 1.493 34 35.0 A-2 35.0 701.0 1.490 8.4 0.003 DI-38 20 A-2 20 40 1.0 1.493 34 42.5 A-2 42.5 85 1.01.491 1.8 0.002

As shown in Table 10, above, increasing the plasticizer content of thecore layer of an interlayer that only included a 3GEH plasticizerreduced the glass transition temperature of the layer, which,ultimately, would have improved its acoustic performance. However, suchan increase also widened the difference between the refractive indicesof the skin and core layers, thereby reducing the optical quality of theinterlayer. As shown by comparison with Disclosed Interlayers DI-30through DI-38 in Table 10, the refractive index of core layersformulated with an additional high refractive index additive, remainedfairly constant with increased plasticizer loading, while stillexhibiting a similar reduction in glass transition temperature. Theresult was an interlayer having core and skin layers with nearly thesame refractive index, which greatly reduced optical defects such asmottle. At the same time, the core layer also exhibited a sufficientlylow glass transition temperature, indicating that the resin also hadacoustic properties.

Example 7 Preparation of Core Layers having Reactive High RefractiveIndex Additives

Several resin layers, used to simulate the inner core layer of amultilayer interlayer, were formed by melt blending a polyvinyln-butyral resin having a residual hydroxyl content of 11 weight percentand a residual acetate content of about 2 weight percent with varyingamounts of 3GEH plasticizer. Comparative Layer CL-16 included 75 phr of3GEH, while Disclosed Layers DL-29 through DL-31 were formulated withvarious mixtures of 3GEH and a reactive high refractive index additive(reactive high RI additive). The reactive high RI additive used inDisclosed Layers DL-29 and DL-30 (Additive A) wasdiphenyldimethoxysilane (commercially available as SID4535.0 fromGelest, Inc., Morrisville, Pa.), and the reactive high RI additive usedin Disclosed Layer DL-31 (Additive B) was phthalic anhydride(commercially available from Sigma Aldrich Co., St. Louis, Mo.). Therefractive index of Comparative Layer CL-16 and each of Disclosed LayersDL-29 through DL-31 was measured and the results are provided in Table11, below.

TABLE 11 Refractive Index of Comparative and Disclosed Core Resin LayersAdditive Additive Plasticizer A B Refractive Resin Content ContentContent Index Layer (phr) (phr) (phr) (nD25) CL-16 75 — — 1.466 DL-29 723 — 1.468 DL-30 72 6 — 1.470 DL-31 72 — 3 1.470

As shown in Table 11, resin layers formed using 3GEH in combination withone or more reactive high refractive index additives had a higherrefractive index than resin layers formulated with only 3GEH. As aresult, when employed as an inner core layer in a multilayer interlayer,the Disclosed Layers DL-29 through DL-31 had a refractive index thatmore closely matched the refractive index of a skin layer formed ofpolyvinyl n-butyral (RI=1.477). As a result, multilayer interlayersformed with Disclosed Layers DL-29 through DL-31 as a core layer exhibitfewer optical defects than multilayer interlayers formed withComparative Layer CL-16 as an inner core layer.

Example 8 Various Interlayers with Resin Blends having a High RefractiveIndex Plasticizer

Two polyvinyl n-butyral resins, R-1 and R-2, were prepared according tothe procedure described above in Example 1. Resin R-1 had a residualhydroxyl content of 19 weight percent, while resin R-2 had a residualhydroxyl content of 11 weight percent. Both resins had residual acetatecontents of 2 weight percent. Several resin blends were prepared thatincluded varying amounts of resins R-1 and R-2 in order to simulatevarious blending rates. The blends were combined with 38 phr of aplasticizer selected from 3GEH (plasticizer P-1; RI=1.442), dioctylphthalate (plasticizer P-2; RI=1.485), a blend of 30 weight percent 3GEHand 70 weight percent Benzoflex® 2088, which is commercially availablefrom Eastman Chemical Company, Kingsport, Tenn., (plasticizer P-3;RI=1.506), and nonylphenyl tetraethylene glycol (plasticizer P-4;RI=1.500). The resulting plasticized resins were then formed into singlesheets that included both resins and the plasticizer. The refractiveindex, haze, and percent visual transmittance was determined for eachsheet and the results are provided in Table 12, below.

TABLE 12 Properties of Several Resin Blends Plasticizer P-1 PlasticizerP-2 Plasticizer P-3 Plasticizer P-4 Resin A Resin B RI of Haze T_(vis)RI of Haze T_(vis) RI of Haze T_(vis) RI of Haze T_(vis) (wt %) (wt %)Interlayer (%) (%) Interlayer (%) (%) Interlayer (%) (%) Interlayer (%)(%) 100 0 1.477 0.4 88.5 1.494 0.4 88.5 1.495 0.3 88.4 1.493 0.3 88.598.9 1.1 1.477 0.6 87.9 1.494 0.4 88.6 1.495 0.3 88.8 1.493 0.3 88.797.8 2.2 1.476 1.2 87.1 1.498 0.3 88.4 1.495 0.3 88.7 1.493 0.2 88.795.6 4.4 1.477 1.9 84.6 1.495 0.4 88.4 1.495 0.3 88.6 1.492 0.4 88.591.2 8.8 1.476 5.4 81.7 1.495 0.5 88.3 1.495 0.4 88.5 1.493 0.3 88.688.9 11.1 1.476 12.9 80.6 1.494 0.6 88.2 1.495 0.4 88.2 1.492 0.4 88.2

As shown in Table 12, above, although blended resin layers formulatedwith plasticizer P-1 maintained a substantially constant refractiveindex with increasing amounts of the lower hydroxyl content resin R-2,the optical properties of these resin blends having high levels of R-2worsened as the amount of R-2 increased. For example, as shown in Table12, the haze of blends that included more than 1.1 percent of resin R-2increased, while the percent visual transmittance of these blendsdecreased from 88.5 percent to 81.7 percent.

In contrast, the resin blends including more than 2.2 percent of resinR-2 that were plasticized with higher refractive index plasticizers P-2through P-4, each exhibited substantially the same haze value andpercent visual transmittance as blends having lower amounts of resinR-2. Therefore, it can be concluded that the resin blends utilizinghigher refractive index plasticizers, such as plasticizers P-2 throughP-4, may permit higher amounts of lower hydroxyl content resins withoutadversely impacting the optical properties of the final blend.

Example 9 Poly(vinyl butyral) Layers including a High Refractive IndexPlasticizer

Several poly(vinyl n-butyral) layers were formed by combining and meltblending three different poly(vinyl n-butyral) resins (PVB-1 throughPVB-3) with different types and amounts of plasticizer. Each of theresins PVB-1 through PBV-3 had a different residual hydroxyl content,ranging from 11 to 20.4 weight percent, and all three resins had aresidual vinyl acetate content of 1 weight percent. Comparative LayersCL-17 through CL-19 were formulated with varying amounts of triethyleneglycol di-(2-ethylhexanoate) (“3GEH”; RI=1.442), while Disclosed LayersDL-32 through DL-37 included a mixture of 3GEH with Benzoflex™ 354(commercially available from Eastman Chemical Company, Kingsport,Tenn.)(RI=1.53). The refractive index of each layer was measured and theresults are summarized in Table 13, below.

TABLE 13 Several Poly(vinyl) Butyral Layers with Various PlasticizersPlasticizer Content Residual Ratio of Total hydroxyl 3GEH Benzoflex ™3GEH to plasticizer Refractive Resin content content 354 Benzoflex ™content Index Layer (wt %) (phr) (phr) 354 (phr) (nD25) CL-17 19 38 — —38 1.477 CL-18 19 38 — — 38 1.477 CL-19 11 75 — — 38 1.466 DL-32 20.430.1 12.9 30/70 43 1.484 DL-33 20.4 25.8 17.2 40/60 43 1.485 DL-34 20.421.5 21.5 50/50 43 1.488 DL-35 11 59.5 25.5 30/70 85 1.479 DL-36 11 5134 40/60 85 1.481 DL-37 11 42.5 42.5 50/50 85 1.486

As shown in Table 13, above, resin layers that included a highrefractive index plasticizer exhibited a higher refractive index thanthose that included only a low refractive index plasticizer.

Example 10 Preparation of Interlayers having High Refractive IndexAdditives

Several of the Comparative and Disclosed Interlayers formed in Example 9and summarized in Table 13, above, were used to create severalComparative and Disclosed Multilayer Interlayers. Each multilayerinterlayer included a pair of outer “skin” layers, each having athickness of 14 mils, sandwiching an inner “core” layer, having athickness of 5 mils, formed of a resin having a lower residual hydroxylcontent. The composition and several properties of the multilayerinterlayers, including total plasticizer content, refractive index,glass transition temperature, mottle, and loss factor, were measured asdescribed above, and the results for the Comparative MultilayerInterlayers CI-20 and CI-21 and Disclosed Multilayer Interlayers DI-39through DI-41 are summarized in Table 14, below.

TABLE 14 Properties of Several Comparative and Disclosed Interlayers ΔTotal Refractive Loss Skin Skin plasticizer Index Refractive Tg FactorInterlayer Layer Core Layer content (Skin- Index (° C.) at No 1 Layer 2(phr) Core) (nD25) Skin Core Mottle 20° C. CI-20 CL-17 CL-18 CL-17 380.000 1.477 30 — 0 0.02 CI-21 CL-17 CL-19 CL-17 42.5 0.011 1.475 35 3 50.32 DI-39 DL-32 DL-35 DL-32 48 0.005 1.484 38.8 2.6 0.4 0.41 DI-40DL-33 DL-36 DL-33 48 0.004 1.486 39.6 4.7 0.4 0.39 DI-41 DL-34 DL-37DL-34 48 0.002 1.488 40.9 8.7 0.4 0.33

As shown in Table 14 above, interlayers formed from skin and core layershaving a refractive index difference greater than 0.010 exhibited moreoptical defects, as shown by the mottle value of 5. Additionally,Disclosed Interlayers DI-39 through DI-41, which utilized a highrefractive index plasticizer, exhibited a higher overall refractiveindex as compared to Comparative Interlayers CI-20 and CI-21, which onlyutilized a plasticizer having a refractive index less than 1.460.

While the invention has been disclosed in conjunction with a descriptionof certain embodiments, including those that are currently believed tobe the preferred embodiments, the detailed description is intended to beillustrative and should not be understood to limit the scope of thepresent disclosure. As would be understood by one of ordinary skill inthe art, embodiments other than those described in detail herein areencompassed by the present invention. Modifications and variations ofthe described embodiments may be made without departing from the spiritand scope of the invention

It will further be understood that any of the ranges, values, orcharacteristics given for any single component of the present disclosurecan be used interchangeably with any ranges, values or characteristicsgiven for any of the other components of the disclosure, wherecompatible, to form an embodiment having defined values for each of thecomponents, as given herein throughout. For example, an interlayer canbe formed comprising poly(vinyl butyral) having a residual hydroxylcontent in any of the ranges given in addition to comprising aplasticizers in any of the ranges given to form many permutations thatare within the scope of the present disclosure, but that would becumbersome to list. Further, ranges provided for a genus or a category,such as phthalates or benzoates, can also be applied to species withinthe genus or members of the category, such as dioctyl terephthalate,unless otherwise noted.

What is claimed is:
 1. An interlayer comprising: a first resin layer,wherein said first resin layer comprises a first poly(vinyl acetal)resin and a first plasticizer, and wherein said first poly(vinyl acetal)resin has a first refractive index; a second resin layer adjacent tosaid first resin layer, wherein said second resin layer comprises asecond poly(vinyl acetal) resin and a second plasticizer, and whereinsaid second poly(vinyl acetal) resin has a second refractive index, athird resin layer adjacent to said second resin layer, wherein saidthird resin layer comprises a third poly(vinyl acetal) resin and a thirdplasticizer, and wherein said third poly(vinyl acetal) resin has a thirdrefractive index, wherein at least one of said first poly(vinyl acetal)resin, said second poly(vinyl acetal) resin, and said third poly(vinylacetal) resin comprises residues of an aldehyde having a refractiveindex of at least 1.421; wherein the difference between the amount ofsaid second plasticizer and amount of at least one of said firstplasticizer and said third plasticizer is at least 8 parts per hundredparts of resin, and wherein the absolute value of the difference betweensaid second refractive index and at least one of said first refractiveindex and said third refractive index is not more than 0.010.
 2. Theinterlayer of claim 1, wherein the difference between the amount of saidsecond plasticizer and the amount of at least one of said firstplasticizer and said third plasticizer is at least 10 parts per hundredparts of resin.
 3. The interlayer of claim 1, wherein the absolute valueof the difference between said second refractive index and at least oneof said first refractive index and said third refractive index is notmore than 0.008.
 4. The interlayer of claim 1, wherein the differencebetween the residual hydroxyl content of said second poly(vinyl acetal)resin and the residual hydroxyl content of at least one of said firstpoly(vinyl acetal) resin and said third poly(vinyl acetal) resin is atleast 2 weight percent and wherein at least one of said first, saidsecond, and said third resin layers has a glass transition temperatureless than 25° C.
 5. The interlayer of claim 1, wherein at least one ofsaid first, said second, and said third resin layers further comprisesat least one aldehyde having a refractive index of less than 1.421. 6.The interlayer of claim 1, wherein said residues of said aldehyde havinga refractive index of at least 1.421 is at least about 0.5 weightpercent, based on the total weight of aldehyde residues of said first,said second, or said third poly(vinyl acetal) resin.
 7. The interlayerof claim 1, wherein at least one of said first, said second and saidthird poly(vinyl acetal) resins has a residual acetate content of atleast 5 weight percent.
 8. The interlayer of claim 1, wherein at leastone of said first, said second, and said third poly(vinyl acetal) resinshas a residual hydroxyl content of at least 16 weight percent and atleast one of said first, said second, and said third poly(vinyl acetal)resins has a residual hydroxyl content of not more than 15 weightpercent, wherein the difference between the glass transition temperatureof said first resin layer and said second resin layer or the differencebetween the glass transition temperature of said second resin layer andsaid third resin layer is at least 3° C.
 9. An interlayer comprising: afirst resin layer, wherein said first resin layer comprises a firstpoly(vinyl acetal) resin and a first plasticizer, and wherein said firstpoly(vinyl acetal) resin has a first refractive index; and a secondresin layer adjacent to said first resin layer, wherein said secondresin layer comprises a second poly(vinyl acetal) resin and a secondplasticizer, and wherein said second poly(vinyl acetal) resin has asecond refractive index, a third resin layer adjacent to said secondresin layer, wherein said third resin layer comprises a third poly(vinylacetal) resin and a third plasticizer, and wherein said third poly(vinylacetal) resin has a third refractive index, wherein at least one of saidfirst poly(vinyl acetal) resin, said second poly(vinyl acetal) resin,and said third poly(vinyl acetal) resin comprises residues of analdehyde having a refractive index of at least 1.421; wherein each ofsaid first and said third poly(vinyl acetal) resins has a residualhydroxyl content of at least 16 weight percent and said secondpoly(vinyl acetal) resin has a residual hydroxyl content of not morethan 15 weight percent, wherein the difference between the glasstransition temperatures of said first and third resin layers and saidsecond resin layer is at least 3° C., and wherein the difference betweenthe residual hydroxyl content of said first and third poly(vinyl acetal)resins and said second poly(vinyl acetal) resin is at least 2 weightpercent, and wherein said second resin layer has a glass transitiontemperature less than 25° C.
 10. The interlayer of claim 9, wherein thedifference between the amount of said second plasticizer and at leastone of said first plasticizer and said third plasticizer is at least 10parts per hundred parts of resin.
 11. The interlayer of claim 9, whereinat least one of said first, said second, and said third resin layersfurther comprises at least one aldehyde having a refractive index ofless than 1.421.
 12. The interlayer of claim 9, wherein at least one ofsaid first, said second and said third poly(vinyl acetal) resins has aresidual acetate content of at least 5 weight percent.
 13. Theinterlayer of claim 9, wherein the absolute value of the differencebetween said second refractive index and at least one of said firstrefractive index and said third refractive index is not more than 0.010.14. The interlayer of claim 9, wherein the absolute value of thedifference between said second refractive index and at least one of saidfirst refractive index and said third refractive index is not more than0.008.
 15. An interlayer comprising: a first resin layer, wherein saidfirst resin layer comprises a first poly(vinyl acetal) resin and a firstplasticizer, and wherein said first poly(vinyl acetal) resin has a firstrefractive index; and a second resin layer adjacent to said first resinlayer, wherein said second resin layer comprises a second poly(vinylacetal) resin and a second plasticizer, and wherein said secondpoly(vinyl acetal) resin has a second refractive index, a third resinlayer adjacent to said second resin layer, wherein said third resinlayer comprises a third poly(vinyl acetal) resin and a thirdplasticizer, and wherein said third poly(vinyl acetal) resin has a thirdrefractive index, wherein at least one of said first poly(vinyl acetal)resin, said second poly(vinyl acetal) resin, and said third poly(vinylacetal) resin comprises residues of an aldehyde having a refractiveindex of at least 1.421; wherein said second poly(vinyl acetal) resinhas a residual hydroxyl content of at least 16 weight percent and eachof said first and third poly(vinyl acetal) resins has a residualhydroxyl content of not more than 15 weight percent, wherein thedifference between the glass transition temperatures of said first andthird resin layers and said second resin layer is at least 3° C., andwherein the difference between the residual hydroxyl content of saidfirst and third poly(vinyl acetal) resins and said second poly(vinylacetal) resin is at least 2 weight percent.
 16. The interlayer of claim15, wherein the difference between the amount of said second plasticizerand at least one of said first plasticizer and said third plasticizer isat least 10 parts per hundred parts of resin.
 17. The interlayer ofclaim 15, wherein at least one of said first, said second, and saidthird resin layers further comprises at least one aldehyde having arefractive index of less than 1.421.
 18. The interlayer of claim 15,wherein at least one of said first, said second and said thirdpoly(vinyl acetal) resins has a residual acetate content of at least 5weight percent.
 19. The interlayer of claim 15, wherein the absolutevalue of the difference between said second refractive index and atleast one of said first refractive index and said third refractive indexis not more than 0.010.
 20. The interlayer of claim 15, wherein theabsolute value of the difference between said second refractive indexand at least one of said first refractive index and said thirdrefractive index is not more than 0.008.